Filed by T-Mobile US, Inc.

pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Sprint Corporation

Commission File No.: 001-04721

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of report (Date of earliest event reported): October 30, 2018

T-MOBILE US, INC.

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (425) 378-4000

(Former Name or Former Address, if Changed Since Last Report):

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the Registrant under any of the following provisions (see General Instructions A.2. below):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR 230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR 240.12b-2).   ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.   ☐

Item 5.07 Submission of Matters to a Vote of Security Holders.

On October 30, 2018, T-Mobile US, Inc. (“T-Mobile”), announced that, following the declaration by the Securities and Exchange Commission on October 29, 2018 that T-Mobile’s registration statement on Form S-4 (No. 333-226435) (the “Registration Statement”) became effective, it received a written consent of Deutsche Telekom Holding B.V., a besloten vennootschap met beperkte aansprakelijkheid organized and existing under the laws of the Netherlands (“DT Holding”), with respect to 538,590,941 shares of common stock of T-Mobile, par value $0.00001 per share (the “T-Mobile Common Stock”), in favor of the proposals summarized below to adopt (1) the share issuance and (2) an amended and restated certificate of incorporation of T-Mobile, as further described below and contemplated by the Business Combination Agreement dated as of April 29, 2018 (the “Business Combination Agreement”), by and among T-Mobile, Huron Merger Sub LLC, a Delaware limited liability company and a wholly owned subsidiary of T-Mobile, Superior Merger Sub Corporation, a Delaware corporation and a wholly owned subsidiary of Huron Merger Sub LLC, Sprint Corporation, a Delaware corporation (“Sprint”), Starburst I, Inc., a Delaware corporation, Galaxy Investment Holdings, Inc., a Delaware corporation, and for the limited purposes set forth therein, Deutsche Telekom AG, an Aktiengesellschaft organized and existing under the laws of the Federal Republic of Germany, DT Holding, and SoftBank Group Corp., a Japanese kabushiki kaisha (“SoftBank”), pursuant to which T-Mobile and Sprint will combine their respective businesses, on the terms and subject to the conditions set forth in the Business Combination Agreement (the “Merger Transactions”). The completion of the Merger Transactions remains subject to regulatory approvals and certain other customary closing conditions, and is expected to occur during the first half of 2019.

The approval of the proposals by 538,590,941 shares of T-Mobile Common Stock pursuant to the written consent of DT Holding constitutes approval by a majority (approximately 63.5%) of the 848,381,358 shares of T-Mobile Common Stock issued and outstanding and entitled to submit written consents as of October 1, 2018, the record date for the submission of written consents. A summary of the proposals, which are described more fully in the joint consent solicitation statement/prospectus that is part of the Registration Statement, is set forth below:

PROPOSAL 1: “Approval of the issuance of shares of T-Mobile common stock in the merger transactions described in the joint consent solicitation statement/prospectus.”

PROPOSAL 2: “Approval of the amendment and restatement of the T-Mobile certificate of incorporation in connection with the merger transactions described in the joint consent solicitation statement/prospectus, including each sub-proposal listed below.”

SUB-PROPOSAL 2(a): “Approval of a sub-proposal to increase in the number of authorized shares of T-Mobile common stock from one billion to two billion, including other amendments incidental or related to the foregoing.”

SUB-PROPOSAL 2(b): “Approval of a sub-proposal to amend the director designation rights of Deutsche Telekom AG and to add director designation rights of SoftBank, including other amendments incidental or related to the foregoing.”

SUB-PROPOSAL 2(c): “Approval of a sub-proposal to add approval rights of SoftBank, including other amendments incidental or related to the foregoing.”

Important Additional Information

In connection with the proposed transaction, T-Mobile US, Inc. (“T-Mobile”) has filed a registration statement on Form S-4 (File No. 333-226435), which contains a joint consent solicitation statement of T-Mobile and Sprint Corporation (“Sprint”), that also constitutes a prospectus of T-Mobile (the “joint consent solicitation statement/prospectus”), and each party will file other documents regarding the proposed transaction with the U.S. Securities and Exchange Commission (the “SEC”). The registration statement on Form S-4 was declared effective by the SEC on October 29, 2018, and T-Mobile and Sprint commenced mailing the joint consent solicitation statement/prospectus to their respective stockholders on October 29, 2018. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE JOINT CONSENT SOLICITATION STATEMENT/PROSPECTUS AND OTHER RELEVANT DOCUMENTS FILED WITH THE SEC WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders may obtain these documents free of charge from the SEC’s website or from T-Mobile or Sprint. The documents filed by T-Mobile may be obtained free of charge at T-Mobile’s website, at www.t-mobile.com, or at the SEC’s website, at www.sec.gov, or from T-Mobile by requesting them by mail at T-Mobile US, Inc., Investor Relations, 1 Park Avenue, 14th Floor, New York, NY 10016, or by telephone at 212-358-3210. The documents filed by Sprint may be obtained free of charge at Sprint’s website, at www.sprint.com, or at the SEC’s website, at www.sec.gov, or from Sprint by requesting them by mail at Sprint Corporation, Shareholder Relations, 6200 Sprint Parkway, Mailstop KSOPHF0302-3B679, Overland Park, Kansas 66251, or by telephone at 913-794-1091.

Participants in the Solicitation

T-Mobile and Sprint and their respective directors and executive officers and other members of management and employees may be deemed to be participants in the solicitation of consents in respect of the proposed transaction. Information about T-Mobile’s directors and executive officers is available in T-Mobile’s proxy statement dated April 26, 2018, for its 2018 Annual Meeting of Stockholders. Information about Sprint’s directors and executive officers is available in Sprint’s proxy statement dated June 26, 2018, for its 2018 Annual Meeting of Stockholders, and in Sprint’s subsequent Current Report on Form 8-K filed with the SEC on July 2, 2018. Other information regarding the participants in the consent solicitation and a description of their direct and indirect interests, by security holdings or otherwise, is contained in the joint consent solicitation statement/prospectus. Investors should read the joint consent solicitation statement/prospectus carefully before making any voting or investment decisions. You may obtain free copies of these documents from T-Mobile or Sprint as indicated above.

No Offer or Solicitation

This communication shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended.

Cautionary Statement Regarding Forward-Looking Statements

This communication contains certain forward-looking statements concerning T-Mobile, Sprint and the proposed transaction between T-Mobile and Sprint. All statements other than statements of fact, including information concerning future results, are forward-looking statements. These forward-looking statements are generally identified by the words “anticipate,” “believe,” “estimate,” “expect,” “intend,” “may,” “could” or similar expressions. Such forward-looking statements include, but are not limited to, statements about the benefits of the proposed transaction, including anticipated future financial and operating results, synergies, accretion and growth rates, T-Mobile’s, Sprint’s and the combined company’s plans, objectives, expectations and intentions, and the expected timing of completion of the proposed transaction. There are several factors which could cause actual plans and results to differ materially from those expressed or implied in forward-looking statements. Such factors include, but are not limited to, the failure to obtain, or delays in obtaining, required regulatory approvals, and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the proposed transaction, or the failure to satisfy any of the other conditions to the proposed transaction on a timely basis or at all; the occurrence of events that may give rise to a right of one or both of the parties to terminate the business combination agreement; adverse effects on the market price of T-Mobile’s or Sprint’s common stock and on T-Mobile’s or Sprint’s operating results because of a failure to complete the proposed transaction in the anticipated timeframe or at all; inability to obtain the financing contemplated to be obtained in connection with the proposed transaction on the expected terms or timing or at all; the ability of T-Mobile, Sprint and the combined company to make payments on debt or to repay existing or future indebtedness when due or to comply with the covenants contained therein; adverse changes in the ratings of T-Mobile’s or Sprint’s debt securities or adverse conditions in the credit markets; negative effects of the announcement, pendency or consummation of the transaction on the market price of T-Mobile’s or Sprint’s common stock and on T-Mobile’s or Sprint’s operating results, including as a result of changes in key customer, supplier, employee or other business relationships; significant transaction costs, including financing costs, and unknown liabilities; failure to realize the expected benefits and synergies of the proposed transaction in the expected timeframes or at all; costs or difficulties related to the integration of Sprint’s network and operations into T-Mobile; the risk of litigation or regulatory actions; the inability of T-Mobile, Sprint or the combined company to retain and hire key personnel; the risk that certain contractual restrictions contained in the business combination agreement during the pendency of the proposed transaction could adversely affect T-Mobile’s or Sprint’s ability to pursue business opportunities or strategic transactions; effects of changes in the regulatory environment in which T-Mobile and Sprint operate; changes in global, political, economic, business, competitive and market conditions; changes in tax and other laws and regulations; and other risks and uncertainties detailed in the Form S-4, as well as in T-Mobile’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and in its subsequent reports on Form 10-Q, including in the sections thereof captioned “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements,” as well as in its subsequent reports on Form 8-K, all of which are filed with the SEC and available at www.sec.gov and www.t-mobile.com. Forward-looking statements are based on current expectations and assumptions, which are subject to risks and uncertainties that may cause actual results to differ materially from those expressed in or implied by such forward-looking statements. Given these risks and uncertainties, persons reading this communication are cautioned not to place undue reliance on such forward-looking statements. T-Mobile assumes no obligation to update or revise the information contained in this communication (whether as a result of new information, future events or otherwise), except as required by applicable law.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.