The information in this prospectus is not complete and may be changed. No securities may be sold until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities, and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

We may offer from time to time:

• Debt securities;
• Shares of our Common Stock;
• Shares of our Preferred Stock; and
• Warrants to purchase any of the other securities that may be sold under this prospectus.

The securities we offer will have an aggregate public offering price of up to $250 million. We will provide specific terms of any offering in supplements to this prospectus. The securities may be offered separately or together in any combination and as separate series. You should read this prospectus and any prospectus supplement carefully before you invest.

We may sell these securities on a continuous or delayed basis directly, through agents, dealers or underwriters as designated from time to time, or through a combination of these methods. We reserve the sole right to accept, and together with any agents, dealers and underwriters, reserve the right to reject, in whole or in part, any proposed purchase of securities. If any agents, dealers or underwriters are involved in the sale of any securities, the applicable prospectus supplement will set forth any applicable commissions or discounts. Our net proceeds from the sale of securities also will be set forth in the applicable prospectus supplement.

Our common stock is listed on the Global Select Market of the NASDAQ Stock Market under the symbol "EGHT."

In this prospectus, "8x8," "we," "us," and "our" refer to 8x8, Inc.

You should rely only on information contained or incorporated by reference in this prospectus. We have not authorized any person to provide you with information that differs from what is contained or incorporated by reference in this prospectus. If any person does provide you with information that differs from what is contained or incorporated by reference in this prospectus, you should not rely on it. This prospectus is not an offer to sell or the solicitation of an offer to buy any securities other than the securities to which it relates, or an offer of solicitation in any jurisdiction where offers or sales are not permitted. The information contained in this prospectus is accurate only as of the date of this prospectus, even though this prospectus may be delivered or shares may be sold under this prospectus on a later date.

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, using a "shelf" registration process. Under the shelf process, we may, from time to time, issue and sell to the public any or all of the securities described in the registration statement in one or more offerings.

This prospectus provides you with a general description of the securities we may offer. Each time we offer securities, we will provide a prospectus supplement that will describe the specific amounts, prices, and terms of the securities we offer. The prospectus supplement also may add, update, or change information contained in this prospectus. This prospectus, together with applicable prospectus supplements, includes all material information relating to this offering. If there is any inconsistency between the information in this prospectus and the information in the accompanying prospectus supplement, you should rely on the information in the prospectus supplement. Please carefully read both this prospectus and any prospectus supplement together with the additional information described below under the section entitled "Where You Can Find More Information."

2

We may sell the securities to or through underwriters, dealers, or agents or directly to purchasers. We and our agents reserve the sole right to accept and to reject in whole or in part any proposed purchase of securities. A prospectus supplement, which we will provide each time we offer securities, will provide the names of any underwriters, dealers or agents involved in the sale of the securities, and any applicable fee, commission, or discount arrangements with them.

Some of the statements in this prospectus constitute forward-looking statements. These statements involve known and unknown risks, uncertainties, and other factors that may cause our or our industry's actual results, levels of activity, performance, or achievements to be materially different from any future results, levels of activity, performance, or achievements expressed or implied by such forward-looking statements. These factors include, among others, those incorporated by reference under "Risk Factors" below.

In some cases, you can identify forward-looking statements by terms such as "may," "will," "should," "expects," "plans," "anticipates," "believes," "estimates," "predicts," "potential," or "continue" or similar terms.

Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance, or achievements. Our actual results could differ materially from those expressed or implied by these forward-looking statements as a result of various factors, including the risk factors incorporated by reference under the heading "Risk Factors" below and a variety of other factors, including, without limitation, statements about our future business operations and results, the market for our technology, our strategy and competition.

Moreover, neither we nor any other person assumes responsibility for the accuracy and completeness of these statements. We undertake no obligation to update or revise any of the forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law. In light of these risks, uncertainties and assumptions, the forward-looking events discussed or incorporated by reference in this prospectus may not occur.

We develop and market telecommunications services for Internet protocol, or IP, telephony and video applications as well as contact center, web-based conferencing and unified communications services, and cloud-based computing services. We offer the 8x8 Virtual Office hosted PBX (private branch exchange) service, 8x8 Virtual Contact Center service, 8x8 Virtual Office Pro unified communications solution and 8x8 Cloud-Based Computing Solutions.

We employ cloud-based technology, known as Voice over Internet Protocol ("VoIP"), to deliver our services. VoIP technology enables communications over the Internet through the compression of voice, video and/or other media into data packets that can be efficiently transmitted over data networks and then converted back into the original media at the other end. Data networks, such as the Internet or local area networks, or LANs, have always utilized packet-switched technology to transmit information between two communicating terminals (for example, a PC downloading a page from a web server, or one computer sending an e-mail message to another computer). IP is the most commonly used protocol for communicating on these packet switched networks. VoIP allows for the transmission of voice, video and data over these same packet-switched networks, providing an alternative to traditional telephone networks which use a fixed electrical path to carry voice signals through a series of switches to a destination.

Our services work over virtually any high-speed Internet connection worldwide to allow calls to or from any phone in the world, whether that phone is an IP phone, a mobile phone or a PSTN phone. Our 8x8 service utilizes IP customer premise equipment to enable plug and play installation and a familiar dial tone user interface. The 8x8 service also uses web-based technologies to enable unified communications services such as web conferencing and Internet fax as well as account setup, account management, billing and customer support. We have developed proprietary implementation of standards-based technologies underlying our 8x8 service, which works with third party carriers to terminate VoIP calls on the PSTN network. As part of the 8x8 service, we currently resell IP telephones and videophones that utilize derivatives of our licensed semiconductor technology and unique software modifications to the protocol and application code that enable them to connect to the 8x8 IP services platform. We continue to enhance and develop new functionality in the software code that is embedded in these devices.

3

Our objective is to provide reliable, scalable, and profitable worldwide Internet-based communications services with unmatched quality by leveraging our patented software technologies to deliver innovative, competitively priced offerings. We intend to bring the best possible voice, video, unified communications, managed hosting and cloud-based computing services at an affordable price to businesses and enhance the ways in which these customers communicate with each other and the world. We intend to continue to focus our marketing primarily towards our business customer services.

We were incorporated in California in February 1987 and reincorporated in Delaware in December 1996. We maintain a corporate Internet website at the address http://www.8x8.com. The contents of this website are not incorporated in or otherwise to be regarded as part of this prospectus. Our principal executive offices are located at 2125 O'Nel Drive, San Jose, CA 95131. Our telephone number at that address is (408) 727-1885.

An investment in our common stock is risky. Prior to making a decision about investing in our common stock, you should carefully consider the specific risks discussed in our other filings with the Securities and Exchange Commission (the "SEC" or the "Commission"), which are incorporated by reference in this prospectus, together with all of the other information contained in this prospectus, any applicable prospectus supplement, or otherwise incorporated by reference in this prospectus. The risks and uncertainties described in our SEC filings are not the only ones facing us. Additional risks and uncertainties not presently known to us, or that we currently see as immaterial, may also harm our business. If any of the risks or uncertainties described in the applicable prospectus supplement or our SEC filings or any such additional risks and uncertainties actually occur, our business, results of operations, cash flows and financial condition could be materially and adversely affected. In that case, the trading price of our common stock could decline, and you might lose all or part of your investment.

If we offer debt securities and/or preference equity securities under this prospectus, then we will, at that time, provide a ratio of earnings to fixed charges and/or ratio of combined fixed charges and preference dividends to earnings, respectively, in a periodic report filed pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, and incorporated into this prospectus by reference.

We intend to use the net proceeds for working capital and other general corporate purposes, including expanding sales and marketing, research and development. We also might use a portion of the net proceeds for the acquisition of technologies, businesses or products that are complementary to our business, although no such acquisitions are subject to any plan or arrangement or being negotiated as of the date of this prospectus, and no portion of the net proceeds has been allocated for any specific acquisition.

The amounts we plan to spend on each area of our operations, including capital expenditures as well as the timing of any expenditures, are determined by internal planning and budgeting processes, and may change over time. Pending such uses, the net proceeds of this offering will be invested according to a cash management policy adopted by our board of directors, which includes short-term, investment-grade securities.

We may offer and sell, at any time and from time to time:

• Our debt securities, in one or more series, which may be senior debt securities or subordinated debt securities, in each case consisting of notes or other unsecured evidences of indebtedness;
• Shares of our common stock, par value $0.001 per share;
• Shares of our preferred stock, par value $0.001 per share;
• Warrants to purchase any of the other securities that may be sold under this prospectus; or
• Any combination of these securities.

4

The terms of any securities we offer will be determined at the time of sale. We may issue debt securities that are exchangeable for and/or convertible into common stock or any of the other securities that may be sold under this prospectus. When particular securities are offered, a supplement to this prospectus will be filed with the SEC, which will describe the terms of the offering and sale of the offered securities.

We may issue debt securities in one or more distinct series. This section summarizes the terms of the debt securities that are common to all series. Most of the financial terms and other specific terms of any series of debt securities that we offer will be described in a prospectus supplement to be attached to the front of this prospectus. Since the terms of specific debt securities may differ from the general information we have provided below, if any information contained in a prospectus supplement contradicts the information below, you should rely on information in the prospectus supplement.

As required by federal law for all bonds and notes of companies that are publicly offered, the debt securities are governed by a document called an "indenture". An indenture is a contract between us and a financial institution acting as trustee of holders of the debt securities on behalf of the holders of the debt securities. The trustee has two main roles. First, the trustee can enforce the rights of holders of the debt securities against us if we default. There are some limitations on the extent to which the trustee acts on behalf of holders of the debt securities, described later under "—Events of Default." Second, the trustee performs certain administrative duties for us.

The debt securities will be either senior debt securities or subordinated debt securities. We will issue the senior debt securities under a senior indenture between us and a trustee. We will issue the subordinated debt securities under a subordinated indenture between us and the same or another trustee. The senior indenture and the subordinated indenture are collectively referred to in this prospectus as the indenture, and each of the trustee under the senior indenture and the trustee under the subordinated indenture are referred to in this prospectus as the trustee. Any debt securities issued by us may be guaranteed by one or more of our subsidiaries. Unless otherwise specified in a prospectus supplement the debt securities will be direct unsecured obligations of 8x8.

Because this section is a summary, it does not describe every aspect of the debt securities and the indenture. We urge you to read the indenture because it, and not this description, defines your rights as a holder of debt securities. For example, in this section, we use capitalized words to signify terms that are specifically defined in the indenture. Some of the definitions are repeated in this prospectus, but for the rest you will need to read the indenture. We have filed the form of the indenture as an exhibit to the registration statement that we have filed with the SEC. See "Where You Can Find More Information," above, for information on how to obtain a copy of the indenture.

Each series of debt securities, unless specified otherwise in the prospectus supplement, will be unsecured obligations of 8x8. Any senior unsecured debt securities that we issue will rank equally with all other unsecured and unsubordinated indebtedness of us. Any subordinated debt securities that we issue will be expressly subordinated in right of payment to the prior payment in full of our senior indebtedness. In addition, unless otherwise specified in the applicable prospectus supplement the debt securities will be structurally subordinated to all existing and future liabilities, including trade payables, of our subsidiaries that do not guarantee the debt securities, and the claims of creditors of those subsidiaries, including trade creditors, will have priority as to the assets and cash flows of those subsidiaries.

Any debt securities proposed to be sold under this prospectus and the attached prospectus supplement ("offered debt securities") and any debt securities issuable upon conversion or exchange of other offered securities ("underlying debt securities"), as well as other unsecured debt securities, may be issued under the indenture in one or more series.

The debt securities of each series will be issued in fully registered form without interest coupons. We currently anticipate that the debt securities of each series offered and sold pursuant to this prospectus will be issued as global debt securities as described under "—Global Securities" and will trade in book-entry form only.

Unless otherwise specified in the applicable prospectus supplement, we will repay the debt securities of each series at 100% of their principal amount, together with accrued and unpaid interest thereon at maturity, except if those debt securities have been previously redeemed or purchased and cancelled.

5

Unless otherwise specified in the applicable prospectus supplement, the debt securities of each series will not be listed on any securities exchange.

The indenture provides that debt securities may be issued under it from time to time in one or more series. For each series of debt securities, this prospectus and the applicable prospectus supplement will describe the following terms and conditions of that series of debt securities:

• the title of the debt securities and whether the debt securities will be senior debt securities or subordinated debt securities of 8x8;
• the total principal amount of the debt securities and any limit on the total principal amount of debt securities of the series;
• the price or prices at which 8x8 will offer the debt securities;
• if not the entire principal amount of the debt securities, the portion of the principal amount payable upon acceleration of the maturity of the debt securities or how this portion will be determined;
• the date or dates, or how the date or dates will be determined or extended, when the principal of the debt securities will be payable;
• the interest rate or rates, which may be fixed or variable, that the debt securities will bear, if any, or how the rate or rates will be determined, the date or dates from which any interest will accrue or how the date or dates will be determined, the interest payment dates, any record dates for these payments and the basis upon which interest will be calculated, if other than that of a 360-day year of twelve 30-day months;
• any optional redemption provisions;
• any sinking fund or other provisions that would obligate us to repurchase or otherwise redeem the debt securities;
• if other than U.S. dollars, the currency or currencies of the debt securities;
• whether the amount of payments of principal, premium or interest, if any, on the debt securities will be determined with reference to an index, formula or other method, which could be based on one or more currencies, commodities, equity indices or other indices, and how these amounts will be determined;
• the place or places, if any, other than or in addition to the city of New York, of payment, transfer, conversion and/or exchange of the debt securities;
• if the denominations in which offered debt securities will be issued are other than denominations of $1,000 or any integral multiple of $1,000;
• the applicability of defeasance provisions of the indenture and any provisions in modification of, in addition to, or in lieu of, any of these provisions;
• any provisions granting special rights to the holders of the debt securities upon the occurrence of specified events;
• any changes or additions to the events of default or covenants contained in the indenture;
• whether the debt securities will be convertible into or exchangeable for any other securities and the applicable terms and conditions of conversion or exchange;
• the terms of any guarantees by any of our subsidiaries;
• subordination provisions, if any, that will apply, to the extent different from those set forth below;

6

• the form of note or other instrument representing the debt if not issued in book entry form; and
• any other terms of the debt securities.

In the applicable prospectus supplement, we will designate the debt securities of a series as being either debt securities bearing interest at a fixed rate of interest or debt securities bearing interest at a floating rate of interest. Each debt security will begin to accrue interest from the date on which it is originally issued. Interest on each debt security will be payable in arrears on the interest payment dates set forth in the applicable prospectus supplement and as otherwise described below and at maturity or, if earlier, the redemption date described below. Interest will be payable to the holder of record of the debt securities at the close of business on the record date for each interest payment date, which record dates will be specified in the applicable prospectus supplement.

As used in the indenture, the term "business day" means, with respect to debt securities of a series, any day, other than a Saturday or Sunday, that is not a day on which banking institutions are authorized or obligated by law or executive order to close in the place where the principal of and premium, if any, and interest on the debt securities of that series are payable.

If the debt securities of a series being offered will bear interest at a fixed rate of interest, the debt securities of that series will bear interest at the annual interest rate specified on the cover page of the applicable prospectus supplement. Interest on those debt securities will be payable semi-annually in arrears on the interest payment dates for those debt securities. If the maturity date, the redemption date or an interest payment date is not a business day, we will pay principal, premium, if any, the redemption price, if any, and interest on the next succeeding business day, and no interest will accrue from and after the relevant maturity date, redemption date or interest payment date to the date of that payment. Unless otherwise specified in the applicable prospectus supplement, interest on the fixed rate debt securities will be computed on the basis of a 360-day year of twelve 30-day months.

If the debt securities of a series being offered will bear interest at a floating rate of interest, the debt securities of that series will bear interest during each relevant interest period at the rate determined as set forth in the applicable prospectus supplement. In the applicable prospectus supplement, we will indicate any spread or spread multiplier to be applied in the interest rate formula to determine the interest rate applicable in any interest period. The applicable prospectus supplement will identify the calculation agent for each series of floating rate debt securities, which will compute the interest accruing on the debt securities of the relevant series.

Principal of and premium, if any, and interest on the debt securities of each series will be payable, and the debt securities may be exchanged or transferred, at the office or agency maintained by us for that purpose (which initially will be the corporate trust office of the trustee). Payment of principal of and premium, if any, and interest on a global security registered in the name of or held by The Depository Trust Company ("DTC") or its nominee will be made in immediately available funds to DTC or its nominee, as the case may be, as the registered holder of that global security. If any of the debt securities are no longer represented by a global security, payment of interest on certificated debt securities in definitive form may, at our option, be made by check mailed directly to holders at their registered addresses. See "—Global Securities."

A holder may transfer or exchange any certificated debt securities in definitive form at the corporate trust office of the trustee. No service charge will be made for any registration of transfer or exchange of debt securities, but we may require payment of a sum sufficient to cover any transfer tax or other similar governmental charge payable in connection therewith.

We are not required to transfer or exchange any debt security selected for redemption for a period of 15 days before mailing of a notice of redemption of the debt security to be redeemed.

The registered holder of debt securities will be treated as the owner of those debt securities for all purposes.

7

All amounts in respect of principal of and premium, if any, or interest on the debt securities paid by us that remain unclaimed two years after that payment was due and payable will be repaid to us, and the holders of those debt securities will thereafter look solely to us for payment.

The supplemental indenture with respect to any particular series of debt securities may contain covenants including, without limitation, covenants restricting or limiting:

• the incurrence of additional debt, including guarantees, by us and our subsidiaries;
• the making of various payments by us and our subsidiaries;
• our business activities and those of our subsidiaries;
• the issuance of other securities by our subsidiaries;
• asset dispositions;
• sale-leaseback transactions;
• transactions with affiliates;
• a change of control;
• the incurrence of liens; and
• mergers and consolidations involving us and our subsidiaries.

For purposes of this prospectus, any reference to the payment of principal of or premium or interest, if any, on debt securities will include additional amounts if required by the terms of the debt securities, subject to the maximum offering amount under this prospectus.

The indenture does not limit the amount of debt securities that may be issued thereunder from time to time. The indenture also provides that there may be more than one trustee thereunder, with respect to one or more different series of indenture securities. See "—Resignation of Trustee," below. At a time when two or more trustees are acting under the indenture, each with respect to only certain series, the term "indenture securities" means the one or more series of debt securities with respect to which each respective trustee is acting. In the event that there is more than one trustee under the indenture, the powers and trust obligations of each trustee described in this prospectus will extend only to the one or more series of indenture securities for which it is trustee. If two or more trustees are acting under the indenture, then the indenture securities for which each trustee is acting would be treated as if issued under separate indentures.

We have the ability to issue indenture securities with terms different from those of indenture securities previously issued and, without the consent of the holders thereof to reopen a previous issue of a series of indenture securities and issue additional indenture securities of that series unless the reopening was restricted when that series was created.

The senior debt securities will rank equally in right of payment with all of our other senior and unsubordinated debt and senior in right of payment to any of our subordinated debt, including the subordinated debt securities. The senior debt securities will be effectively subordinated to all of our secured debt and to all debt, including trade debt, of our subsidiaries, except as to subsidiaries that guaranty the debt. We will disclose the amount of our secured debt in the prospectus supplement.

The subordinated debt securities will rank junior in right of payment to all of our senior indebtedness. Senior indebtedness will be defined to include all notes or other evidences of debt not expressed to be subordinate or junior in right of payment to any of our other debt. The debt will be structurally subordinated to all debt, including trade debt, of our subsidiaries, except as to subsidiaries that guaranty the debt.

8

If the offered securities are subordinated debt securities, the supplemental indenture may provide that no cash payment of principal, interest and any premium on the subordinated debt securities may be made:

• if we fail to pay when due any amounts on any senior indebtedness;
• if our property or we are involved in any voluntary or involuntary liquidation or bankruptcy; and
• in other instances specified in the supplemental indenture.

If any series of our debt securities are convertible or exchangeable, the applicable prospectus supplement will specify:

• the type of securities into which it may be converted or exchanged;
• the conversion price or exchange ratio, or its method of calculation; and
• how the conversion price or exchange ratio may be adjusted if our debt securities are redeemed.

Unless otherwise specified in the applicable prospectus supplement, the following will be events of default with respect to any series of debt securities or guaranties:

• default for 30 days in the payment when due of interest on the debt securities;
• default in payment when due of the principal of or any premium on the debt securities;
• default in the performance of or breach of various covenants after applicable notice and/or grace period; and
• various events of bankruptcy or insolvency with respect to us.

The applicable prospectus supplement will describe any additional events of default.

If an event of default occurs with respect to debt securities of a series then outstanding and is continuing, then the trustee or the holders of not less than 25% in principal amount of the debt securities of that series then outstanding, by a notice in writing to 8x8 (and to the trustee if given by the holders), may, and the trustee at the request of such holders shall, declare the principal amount (or, if the debt securities of that series are original issue discount securities, such portion of the principal amount as may be specified in the terms of that series) of, premium, if any, and accrued interest on all of the debt securities of that series to be due and payable immediately, and the same (or specified portion thereof) shall become immediately due and payable. A declaration of default under the indenture or under other payment obligations could give rise to cross-defaults and acceleration with respect to the debt securities or such other payment obligations.

At any time after a declaration of acceleration with respect to debt securities of any series (or of all series, as the case may be) has been made and before a judgment or decree for payment of the money due has been obtained by the trustee as provided in the indenture, the holders of a majority in principal amount of the debt securities of that series (or of all series, as the case may be) then outstanding, by written notice to 8x8 and the trustee, may rescind such declaration and its consequences under the circumstances specified in the applicable debenture.

The indenture will provide that no such rescission shall affect all subsequent default or impair any right consequent thereon.

With respect to the debt securities of any series, the holders of not less than a majority in principal amount of the debt securities of such series then outstanding shall have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, provided that:

• such direction shall not be in conflict with any rule of law or with the indenture;
• the trustee may take any other action deemed proper by the trustee which is not inconsistent with such direction; and

9

• the trustee need not take any action which might involve it in personal liability or be unjustly prejudicial to the holders of debt securities of such series not consenting.

No holder of any debt security of any series or any related coupons shall have any right to institute any proceeding, judicial or otherwise, with respect to the indenture, or for the appointment of a receiver or trustee, or for any other remedy hereunder, unless:

• the holder has previously given written notice to the trustee of a continuing event of default with respect to the debt securities of that series;
• the holders of not less than 25% in principal amount of the debt securities of that series then outstanding shall have made written request to the trustee to institute proceedings in respect of the event of default in its own name as trustee under the indenture;
• such holder or holders have offered to the trustee indemnity reasonably satisfactory to the trustee against the costs, expenses and liabilities to be incurred in compliance with such request;
• the trustee for 90 days after its receipt of such notice, request and offer of indemnity has failed to institute any such proceeding; and
• no direction inconsistent with such written request has been given to the trustee during such 90-day period by the holders of a majority or more in principal amount of the debt securities of that series then outstanding.

However, no holder of a debt security has the right under the indenture to affect, disturb or prejudice the rights of any other holders of debt securities of the same series, or to obtain or to seek to obtain priority or preference over any other of such holders or to enforce any right under the indenture, except in the manner provided in the indenture and for the equal and ratable benefit of all holders of debt securities of the same series.

Every year we will be required to deliver to the trustee a certificate as to our performance of our obligations under the indenture and as to any defaults.

10

Mergers, Consolidations and Certain Sale of Assets

The indenture provides that we may consolidate with or merge with or into any other person, and may sell, transfer, lease or convey all or substantially all of our properties and assets to another person, provided that the following conditions are satisfied:

• we are the continuing entity, or the resulting, surviving or transferee person (the "Successor") is a corporation, partnership, trust or other entity organized and validly existing under the laws of any domestic or foreign jurisdiction and the Successor (if not us) will expressly assume, by supplemental indenture, all of our obligations under the debt securities and the indenture and, for each security that by its terms provides for conversion, provide for the right to convert that security in accordance with its terms;
• immediately after giving effect to that transaction, no default or event of default under the indenture has occurred and is continuing; and
• the trustee receives from us an officer's certificate and an opinion of counsel that the merger, consolidation, transfer, sale, lease or conveyance and the supplemental indenture, as the case may be, complies with the applicable provisions of the indenture.

If we consolidate or merge with or into any other person or sell, transfer, lease or convey all or substantially all of our properties and assets in accordance with the indenture, the Successor will be substituted for us under the indenture, with the same effect as if it had been an original party to the indenture. As a result, the Successor may exercise our rights and powers under the indenture, and we will be released from all our liabilities and obligations under the indenture and the debt securities.

Any substitution of the Successor for us might be deemed for federal income tax purposes to be an exchange of the debt securities for "new" debt securities, resulting in recognition of gain or loss for those purposes and possibly certain other adverse tax consequences to beneficial owners of the debt securities. Holders should consult their own tax advisors regarding the tax consequences of any substitution.

For purposes of this covenant, "person" means any individual, corporation, partnership, limited liability company, joint venture, association, joint-stock company, trust, unincorporated organization or government or any agency or political subdivision thereof or any other entity.

Modification and Waiver

The indenture will provide that 8x8 and the trustee may amend or supplement the indenture or the debt securities without notice to or the consent of any holder for clarification, corrections, and legal compliance purposes, including as follows:

• to cure any ambiguity, defect or inconsistency;
• to provide for uncertificated debt securities in addition to or in place of certificated debt securities;
• to make any change that does not adversely affect the interests thereunder of any holder;
• to qualify the indenture under the Trust Indenture Act of 1939 as amended or to comply with the requirements of the Securities and Exchange Commission in order to maintain the qualification of the indenture under the Trust Indenture Act;
• to evidence the succession of another person to 8x8 and that person's assumption of 8x8's covenants;
• to add to 8x8's covenants;
• to add any additional events of default;
• to add one or more guarantees for the benefit of holders of the debt securities;
• to secure the debt securities pursuant to the covenants of the indenture;
• to establish the form or terms of debt securities;
• to evidence the appointment of a successor trustee under the indenture;
• to comply with the rules of any applicable securities depository;

11

• to comply with requirements of the SEC in order to effect or maintain the qualification of the indenture under the Trust Indenture Act of 1939, as amended;
• to close the indenture with respect to authentication and delivery of additional series of debt securities;
• to conform any provision of the indenture, any supplemental indenture, one or more series of debt securities or any related guarantees or security documents to the description of such securities contained in our prospectus, prospectus supplement, offering memorandum or similar document with respect to the offering of the securities of such series to the extent that such description was intended to be a verbatim recitation of a provision in the indenture, such securities or any related guarantees or security documents, as provided in an officer's certificate; or
• to supplement the indenture in order to permit the defeasance and discharge of any series of debt securities.

The indenture will provide that 8x8 and the trustee may make modifications and amendments to the indenture, and waive past defaults, with the consent of the holders of not less than a majority in aggregate principal amount at maturity of the outstanding debt securities in a series; provided, however, that no such modification or amendment may, without the consent of each holder affected thereby,

• change the stated maturity of the principal of, or any installment of interest on, any debt security;
• reduce the principal amount of, or premium, if any, or interest on, any debt security;
• reduce the amount of a debt security's principal that would be due and payable upon a declaration of acceleration, following a default;
• change the place of payment of, the currency of payment of principal of, or premium, if any, or interest on, any debt security;
• impair the right to institute suit for the enforcement of any payment on or after the stated maturity (or, in the case of a redemption, on or after the redemption date) of any debt security;
• adversely affect any right to convert or exchange any debt security that is convertible or exchangeable;
• make any change that adversely affects in any material respect the right to convert or exchange any debt security or decreases the conversion or exchange rate or increases the conversion price of any convertible or exchangeable debt security, unless that decrease or increase is permitted by the terms of the debt securities; or
• reduce the stated percentage of outstanding debt securities the consent of whose holders is necessary to modify, or amend the indenture or waive a past default.

Any issued debt securities and the indenture will be governed by the laws of the state of New York.

The indenture will provide that, except during the continuance of an event of default or default, the trustee will not be liable, except for the performance of such duties as are specifically set forth in such indenture. If an event of default has occurred and is continuing, the trustee will use the same degree of care and skill in its exercise as a prudent person would exercise under the circumstances in the conduct of such person's own affairs.

The indenture and provisions of the Trust Indenture Act incorporated by reference in the indenture contain limitations on the rights of the trustee, should it become our creditor, to obtain payment of claims in certain cases or to realize on certain property received by it in respect of any such claims, as security or otherwise. The trustee is permitted to engage in other transactions; provided, however, that if it acquires any conflicting interest, it must eliminate such conflict or resign.

12

Defeasance

The following provisions will be applicable to each series of debt securities unless we state in the applicable prospectus supplement that the provisions of covenant defeasance and full defeasance will not be applicable to that series.

The indenture will provide that we will be deemed to have paid and will be discharged from any and all obligations in respect of any issued series of debt securities and the provisions of the indenture, or will be released from our obligations to comply with covenants relating to those debt securities as described above or in the applicable prospectus supplement, (which may include obligations concerning subordination of our subordinated debt securities) upon satisfaction of applicable specified conditions such as--

• We have irrevocably deposited with the trustee, in trust, money and/or U.S. Government Obligations (as defined in the indenture) that through the payment of interest and principal in respect of those monies and/or U.S. Government Obligations in accordance with their terms, will provide money in an amount sufficient to pay the principal of, premium, if any, and interest, if any, on the series of debt securities on the stated maturity of such payments and any applicable sinking fund or analogous payments in accordance with the terms of the indenture and the debt securities;
• Such defeasance shall not result in a breach, or constitute a default, under the indenture or any other material agreement of 8x8;
• We have delivered to the trustee either (i) an opinion of counsel to the effect that holders will not recognize additional income, gain or loss for U.S. federal income tax purposes as a result of 8x8's exercise of the defeasance or covenant defeasance, or (ii) a ruling directed to the trustee received from the Internal Revenue Service to the same effect as the aforementioned opinion of counsel;
• 8x8 has delivered to the trustee an officer's certificate and an opinion of counsel, each stating that all the conditions precedent to full defeasance have been complied with.

In the event we exercise our option to omit compliance with certain covenants and provisions of the indenture with respect to a series of debt securities and the debt securities are declared due and payable because of the occurrence of an event of default that remains applicable, the amount of money and/or U.S. Government Obligations on deposit with the trustee will be sufficient to pay amounts due on the debt securities at the time of their stated maturity but may not be sufficient to pay amounts due on the debt securities at the time of the acceleration resulting front such event of default, however, we will remain liable for such payments.

We cannot defease our obligations to register the transfer or exchange of our debt securities; to replace our debt securities that have been stolen, lost or mutilated; to maintain paying agencies; or to hold fund for payment in trust. We may not defease our obligations if there is a continuing event of default on securities issued under the applicable indenture, or if depositing amounts into trust would cause the trustee to have conflicting interests with respect to other of our securities.

Each trustee may resign or be removed with respect to one or more series of indenture securities provided that a successor trustee is appointed to act with respect to these series. In the event that two or more persons are acting as trustee with respect to different series of indenture securities under one of the indentures, each of the trustees will be a trustee of a trust separate and apart from the trust administered by any other trustee.

We may issue debt securities as registered securities in book-entry form only. A global security represents one or any other number of individual debt securities. All debt securities represented by the same global security have the same terms.

Each debt security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, The

13

Depository Trust Company, New York, New York, known as DTC, will be the depositary for all debt securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary or its nominee, unless special termination situations arise. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all debt securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that has an account with the depositary. Thus, an investor whose security is represented by a global security will not be a holder of the debt security, but only an indirect holder of a beneficial interest in the global security.

As an indirect holder, an investor's rights relating to a global security will be governed by the account rules of the investor's financial institution and of the depositary, as well as general laws relating to securities transfers. The depositary that holds the global security will be considered the holder of the debt securities represented by the global security.

If debt securities are issued only in the form of a global security, an investor should be aware of the following:

• An investor cannot cause the debt securities to be registered in his or her name, and cannot obtain certificates for his or her interest in the debt securities, except in the special situations we describe below.
• An investor will be an indirect holder and must look to his or her own bank or broker for payments on the debt securities and protection of his or her legal rights relating to the debt securities.
• An investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the debt securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective.
• The depositary's policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor's interest in a global security. We and the trustee have no responsibility for any aspect of the depositary's actions or for its records of ownership interests in a global security. We and the trustee also do not supervise the depositary in any way.
• DTC requires that those who purchase and sell interests in a global security deposited in its book-entry system use immediately available funds. Your broker or bank may also require you to use immediately available funds when purchasing or selling interests in a global security.
• Financial institutions that participate in the depositary's book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the debt security. There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Generally, a global security will be terminated and interests in it will be exchanged for certificates in non-global form, referred to as certificated securities only in the following instances:

• if the depositary notifies us and the trustee that it is unwilling or unable to continue as depositary for that global security;
• if the depositary ceases to be a clearing agency and we do not appoint another institution to act as depositary within 90 days;
• if we determine that we wish to terminate that global security; or
• if an event of default has occurred with regard to the debt securities represented by that global security and has not been cured or waived, and the owner of beneficial interests in the global security requests that certificated securities be delivered; we discuss defaults above under "Events of Default."

The prospectus supplement may list situations for terminating a global security that would apply only to the particular series of debt securities covered by the prospectus supplement. If a global security is terminated, only the depositary, and not we or the applicable trustee, is responsible for deciding the names of the institutions in whose

14

names the debt securities represented by the global security will be registered and, therefore, who will be the holders of those debt securities.

Unless specified otherwise in a prospectus supplement, in the event certificated registered debt securities are issued, the holders of certificated registered debt securities will be able to receive payments of principal and of interest on their debt securities at the office of the paying agent. All payments of interest may be received at the offices of such paying agent upon presentation of certificated debt securities and all payments of principal may be received at such offices upon surrender of the debt securities. We also have the option of mailing checks or making wire transfers to the registered holders of the debt securities. Unless specified otherwise in a prospectus supplement, we will maintain a paying agent for the debt securities in the city of New York at all times that payments are to be made in respect of the debt securities and, if and so long as the debt securities remain outstanding.

Our authorized capital stock consists of 200,000,000 shares of common stock, par value $0.001 per share, and 5,000,000 shares of preferred stock, par value $0.001 per share.

As of February 28, 2013, 72,103,171 shares of our common stock were outstanding and held of record by 261 stockholders. Each holder of our common stock is entitled to--

• one vote per share on all matters submitted to a vote of the stockholders;
• dividends as may be declared by our board of directors out of funds legally available for that purpose, subject to the rights of any preferred stock that may be outstanding; and
• his, her or its pro rata share in any distribution of our assets after payment or providing for the payment of liabilities and the liquidation preference of any outstanding preferred stock in the event of liquidation.

Holders of common stock have no cumulative voting rights, redemption rights or preemptive rights to purchase or subscribe for any shares of our common stock or other securities. All of the outstanding shares of common stock are fully paid and nonassessable. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

Our board of directors has the authority, subject to any limitations prescribed by Delaware law, to issue shares of preferred stock in one or more series and to fix and determine the relative rights and preferences of the shares constituting any series to be established, without any further vote or action by the stockholders. Any shares of our preferred stock so issued may have priority over our common stock with respect to dividend, liquidation, redemption, voting and other rights.

Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of our common stock. Although the issuance of preferred stock could provide us with flexibility in connection with possible acquisitions and other corporate purposes, under some circumstances, it could have the effect of delaying, deferring or preventing a change of control.

The prospectus supplement will specify as to each issuance of preferred stock:

• the maximum number of shares;
• the designation of the shares;

15

• annual dividend rate, if any, whether the dividend rate is fixed or variable, the date dividends will accrue, the dividend payment dates and whether dividends will be cumulative;
• the price and the terms and conditions for redemption, if any, including redemption at our option or at the option of the holders, including the time period for redemption, and any accumulated dividends or premiums;
• the liquidation preference, if any, and any accumulated dividends upon the liquidation, dissolution or winding up of our affairs;
• any sinking fund or similar provision, and, if so, the terms and provisions relating to the purpose and operation of the fund;
• the terms and conditions, if any, for conversion or exchange of shares into or for any other class or classes of our capital stock or any series of any other class or classes, or into or for any other series of the same class, or any other securities or assets, including the price or the rate of conversion or exchange and the method, if any, of adjustment;
• the voting rights; and
• any or all other preferences and relative, participating, optional or other special rights, privileges or qualifications, limitations or restrictions.

Preferred stock will be fully paid and nonassessable upon issuance. The preferred stock or any series of preferred stock may be represented, in whole or in part, by one or more global certificates, which will represent an aggregate number of shares equal to that of the preferred stock represented by the global certificate.

Each global certificate will:

• be registered in the name of a depositary or a nominee of the depositary identified in the prospectus supplement;
• be deposited with such depositary or nominee or a custodian for the depositary; and
• bear a legend regarding any restrictions on exchanges and registration of transfer and any other matters as may be provided for under the certificate of designations.

Certain provisions of our charter documents and Delaware law could have an anti-takeover effect and could delay, discourage or prevent a tender offer or takeover attempt that a stockholder might consider to be in its best interests, including attempts that might otherwise result in a premium being paid over the market price of our common stock.

Certificate of Incorporation and Bylaws. Our certificate of incorporation provides that stockholders can take action only at a duly called annual or special meeting of the stockholders and not by written consent. At the same time, our bylaws will provide that special meetings of stockholders may be called only by our chairman of the board, our chief executive officer, any officer at the request in writing of a majority of the directors or by the holders of at least a majority of our outstanding voting shares. These provisions could delay consideration of a stockholder proposal until the next annual meeting.

Our bylaws provide for an advance notice procedure for the nomination, other than by or at the direction of our board of directors, of candidates for election as directors, as well as for other stockholder proposals to be considered at annual meetings of stockholders. In addition, under our bylaws newly created directorships resulting from any increase in the number of directors or any vacancies in the board resulting from death, resignation, retirement, disqualification, removal from office or other cause during a director's term in office can be filled by the vote of the remaining directors in office, and the board is expressly authorized to amend the bylaws without stockholder consent. These provisions may preclude a third party from removing incumbent directors and gaining control of our board of directors. Accordingly, these provisions could discourage a third party from initiating a proxy contest, making a tender offer or otherwise attempting to gain control of our company.

Delaware Takeover Statute. Section 203 of the Delaware General Corporation Law, or DGCL, generally prohibits a publicly-held Delaware corporation from engaging in an acquisition, asset sale or other transaction resulting in a financial benefit to any person who, together with affiliates and associates, owns, or within three years did own,

16

15% or more of a corporation's voting stock. The prohibition continues for a period of three years after the date of the transaction in which the person becomes an owner of 15% or more of the corporation's voting stock, unless the business combination is approved in a prescribed manner. The statute could prohibit, delay, defer or prevent a change in control with respect to our company.

The transfer agent and registrar for our common stock is Computershare Limited. We plan to retain the same transfer agent and registrar for any series of our preferred stock.

The following description, together with the additional information we include in any applicable prospectus supplement, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and any related warrant agreements and warrant certificates. While the terms we have summarized below will apply generally to any warrants we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement, which may differ from the terms we describe below.

We may issue, together with other securities or separately, warrants to purchase our preferred stock, common stock or other securities. We may issue the warrants directly to the purchasers of the warrants or under warrant agreements to be entered into between us and a bank or trust company, as warrant agent, all as set forth in the applicable prospectus supplement. A warrant agent will act solely as our agent in connection with the warrants of the series being offered and will not assume any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants.

The prospectus supplement will describe the following terms, where applicable, of warrants that we may offer:

• the title of the warrants;
• the designation, amount and terms of the securities for which the warrants are exercisable and the procedures and conditions relating to the exercise of such warrants;
• the designation and terms of the other securities, if any, with which the warrants are to be issued and the number of warrants issued with each such security;
• the price or prices at which the warrants will be issued;
• the aggregate number of warrants;
• any provisions for adjustment of the number or amount of securities receivable upon exercise of the warrants or the exercise price of the warrants;
• the price or prices at which the securities purchasable upon exercise of the warrants may be purchased, including provisions for adjustment of the exercise price of the warrant;
• if applicable, the date on and after which the warrants and the securities purchasable upon exercise of the warrants will be separately transferable;
• if applicable, a discussion of the material U.S. federal income tax considerations applicable to the exercise of the warrants;
• any other terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants;
• the date on which the right to exercise the warrants shall commence, and the date on which the right shall expire; and
• the maximum or minimum number of warrants which may be exercised at any time.

17

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Each warrant will entitle the holder thereof to purchase for cash the amount of debt securities or number of shares of preferred stock or common stock at the exercise price as will in each case be set forth in, or be determinable as set forth in, the applicable prospectus supplement. Warrants may be exercised at any time up to the close of business on the expiration date set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Warrants may be exercised as set forth in the applicable prospectus supplement relating to the warrants offered thereby. Upon receipt of payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will, as soon as practicable, forward the purchased securities. If less than all of the warrants represented by the warrant certificate are exercised, a new warrant certificate will be issued for the remaining warrants.

Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, that holder's warrants.

We may sell the securities in and outside the United States through underwriters or dealers, directly to purchasers, including our affiliates, through agents, or through a combination of any of these methods. The prospectus supplement will include the following information:

• the terms of the offering;
• the names of any underwriters or agents;
• the name or names of any managing underwriter or underwriters;
• the purchase price of the securities;
• the net proceeds from the sale of the securities;
• any delayed delivery arrangements;
• any underwriting discounts, commissions and other items constituting underwriters' compensation;
• any initial public offering price;
• any discounts or concessions allowed or reallowed or paid to dealers; and
• any commissions paid to agents.

If underwriters are used in the sale of any of these securities, the underwriters will acquire the securities for their own account. The underwriters may resell the securities from time to time in one or more transactions, including negotiated transactions, at a fixed public offering price or at varying prices determined at the time of sale. Underwriters may offer securities to the public either through underwriting syndicates represented by one or more managing underwriters or directly by one or more firms acting as underwriters. Unless we inform you otherwise in

18

any prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions, and the underwriters will be obligated to purchase all the offered securities if they purchase any of them. The underwriters may change from time to time any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers.

During and after an offering through underwriters, the underwriters may purchase and sell the securities in the open market. These transactions may include overallotment and stabilizing transactions and purchases to cover syndicate short positions created in connection with the offering. The underwriters may also impose a penalty bid, which means that selling concessions allowed to syndicate members or other broker-dealers for the offered securities sold for their account may be reclaimed by the syndicate if the offered securities are repurchased by the syndicate in stabilizing or covering transactions. These activities may stabilize, maintain or otherwise affect the market price of the offered securities, which may be higher than the price that might otherwise prevail in the open market. If commenced, the underwriters may discontinue these activities at any time.

Some or all of the securities that we offer though this prospectus may be new issues of securities with no established trading market. Any underwriters to whom we sell these securities for public offering and sale may make a market in those securities, but they will not be obligated to and they may discontinue any market making at any time without notice. Accordingly, we cannot assure you of the liquidity of, or continued trading markets for, any securities that we offer.

If dealers are used in the sale of securities, we will sell the securities to them as principals. They may then resell those securities to the public at varying prices determined by the dealers at the time of resale. We will include in the prospectus supplement the names of the dealers and the terms of the transaction.

We may sell the securities directly, and not through underwriters or agents. We may also sell the securities through agents designated from time to time. In the prospectus supplement, we will name any agent involved in the offer or sale of the offered securities, and we will describe any commissions payable to the agent. Unless we inform you otherwise in the prospectus supplement, any agent will agree to use its reasonable best efforts to solicit purchases for the period of its appointment.

We may sell the securities directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act of 1933, as amended (the "Securities Act"), with respect to any sale of those securities. We will describe the terms of any such sales in the prospectus supplement.

If we so indicate in the prospectus supplement, we may authorize agents, underwriters or dealers to solicit offers from certain types of institutions to purchase securities from us at the public offering price under delayed delivery contracts. These contracts would provide for payment and delivery on a specified date in the future. The contracts would be subject only to those conditions described in the prospectus supplement. The prospectus supplement will describe the commission payable for solicitation of those contracts.

We may also offer and sell our common stock upon the exercise of warrants issued by us, pursuant to the exemption from the registration requirements of the Securities Act provided by Section 3(a)(10) of the Securities Act, in connection with a settlement of litigation against us. No underwriter would be used in connection with such offer and sale of common stock or the exercise of such warrants. We would issue the shares of our common stock directly to the holders of such warrants, upon the exercise of such warrants, from time to time. We will describe the terms of any such offers, sales and warrants in a prospectus supplement.

We may have agreements with the agents, dealers and underwriters to indemnify them against certain civil liabilities, including liabilities under the Securities Act, or to contribute with respect to payments that the agents, dealers or underwriters may be required to make. Agents, dealers and underwriters may be customers of, engage in transactions with or perform services for us in the ordinary course of their businesses.

19

The validity of the issuance of shares of common stock offered hereby will be passed upon for us by Bingham McCutchen LLP, Palo Alto, California.

The consolidated financial statements of 8x8 as of March 31, 2012 and 2011, and for each of the three years in the period ended March 31, 2012, and the effectiveness of internal control over financial reporting as of March 31, 2012, have been incorporated by reference herein in reliance upon the report of Moss Adams LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing. To the extent that Moss Adams LLP audits and reports on consolidated financial statements of 8x8 at future dates and consents to the use of their reports thereon, such consolidated financial statements also will be incorporated by reference in the registration statement in reliance upon their reports and said authority.

We file annual, quarterly and special reports and other information with the SEC. In addition, we have filed with the SEC a Registration Statement on Form S-3, of which this prospectus is a part, under the Securities Act, with respect to the shares of common stock offered hereby. You may read and obtain copies at prescribed rates of any document that we file with the SEC at its Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the Public Reference Room. Our SEC filings are also available to you free of charge at the SEC's web site at http://www.sec.gov, which contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC.

Our common stock is traded on the Global Select Market of the NASDAQ Stock Market. Material filed by us can be inspected at the offices of the Financial Industry Regulatory Authority, 1735 K Street, N.W., Washington, D.C. 20006.

The SEC allows us to "incorporate by reference" the information we file with them, which means that we can disclose important information by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below:

20

In addition, all documents filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of filing the registration statement that includes this prospectus and prior to the filing of a post-effective amendment to the registration statement containing this prospectus, which indicates that all securities offered have been sold or which deregisters all of such securities then remaining unsold, shall be deemed to be incorporated by reference in this prospectus and to be a part hereof from the respective dates of filing of such documents. You may request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:

8x8, Inc.
2125 O'Nel Drive
San Jose, CA 95131(408) 727-1885
Attention: Chief Financial Officer

In addition, you may obtain a copy of these filings from the SEC as described above in the section entitled "Where You Can Find More Information."

21

As permitted by the DGCL, our bylaws provide that we shall indemnify our directors and officers, and may indemnify our employees and other agents, to the fullest extent permitted by law. The bylaws also permit us to secure insurance on behalf of any officer, director, employee or agent of another corporation, partnership, joint venture, trust or other enterprise against any liability arising out of his or her actions in that capacity if he or she is serving at our request. We have obtained officer and director liability insurance with respect to liabilities arising out of various matters, including matters arising under the Securities Act.

We have entered into agreements with our directors that, among other things, indemnify them for certain expenses (including attorneys' fees), judgments, fines and settlement amounts incurred by them in any action or proceeding, including any action by us or in our right, arising out of the person's services as a director or officer of ours or any other company or enterprise to which the person provides services at our request.

II-1

Item 16. Exhibits.

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints Bryan Martin and Dan Weirich, and each one of them, acting individually and without the other, as his or her attorney-in-fact, each with full power of substitution, for him in any and all capacities, to sign any and all amendments to this Registration Statement (including post-effective amendments), and to sign any registration statement for the same offering covered by this Registration Statement that is to be effective upon filing pursuant to Rule 462(b) promulgated under the Securities Act of 1933, and all post-effective amendments thereto, and to file the same, with exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, hereby ratifying and confirming all that each of said attorneys-in-fact or his substitute or substitutes may do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.