EX-5.1

Exhibit 5.1

[Letterhead of Wachtell, Lipton, Rosen & Katz]

[ ], 2018

T-Mobile US, Inc.

12920 SE 38th Street

Bellevue, Washington 98006-1350

Re:

Registration Statement on Form S-4 (File No. 333-226435)

Ladies and Gentlemen:

We have acted as special counsel to T-Mobile US, Inc., a Delaware corporation (“T-Mobile”), in connection with the preparation and filing of T-Mobile’s Registration Statement on Form S-4 (the “Registration Statement,” which term does not include any other document or agreement whether or not specifically referred to therein or attached as an exhibit or schedule thereto), relating to shares of T-Mobile’s common stock, par value $0.00001 per share (the “T-Mobile Shares”), to be issued by T-Mobile pursuant to the terms of the Business Combination Agreement (the “Business Combination Agreement”), dated as of April 29, 2018, by and among T-Mobile, Sprint Corporation, Huron Merger Sub LLC, Superior Merger Sub Corporation, Starburst I, Inc., Galaxy Investment Holdings, Inc., and for the limited purposes set forth therein, Deutsche Telekom AG, Deutsche Telekom Holding B.V. and SoftBank Group Corp.

For purposes of giving this opinion, we have examined the Registration Statement, the Business Combination Agreement, T-Mobile’s Fourth Amended and Restated Certificate of Incorporation, T-Mobile’s Fifth Amended and Restated Bylaws and forms of T-Mobile’s Fifth Amended and Restated Certificate of Incorporation and T-Mobile’s Sixth Amended and Restated Bylaws, each of which is proposed in connection with the Business Combination Agreement. We have also examined the originals, or duplicates or certified or conformed copies, of such corporate records, agreements, documents and other instruments and have made such other investigations as we have deemed relevant and necessary in connection with this opinion. As to questions of fact material to this opinion, we have relied, with your approval, upon oral and written representations of T-Mobile and certificates or comparable documents of public officials and of officers and representatives of T-Mobile.

In making such examination and rendering this opinion, we have assumed without verification the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the authenticity of the originals of such documents submitted to us as certified copies, the conformity to originals of all documents submitted to us as copies, the authenticity of the originals of such documents, that all documents submitted to us as certified copies are true and correct copies of such originals and the legal capacity of all individuals executing any of the foregoing documents.

Based upon and subject to the foregoing examination and in reliance thereon, and subject to the qualifications, assumptions and limitations stated herein and in reliance on statements of fact contained in the documents that we have examined or reviewed, we are of the opinion that the T-Mobile Shares to be issued by T-Mobile pursuant to and in the manner contemplated by the terms of the Business Combination Agreement will be, upon issuance, duly authorized and, when the Registration Statement has been declared effective by order of the Securities and Exchange Commission and the T-Mobile Shares have been issued and paid for in the manner contemplated by and upon the terms and conditions set forth in the Registration Statement and the Business Combination Agreement, such T-Mobile Shares will be validly issued, fully paid and nonassessable.

We are members of the bar of the State of New York. T-Mobile is a Delaware corporation, and we have not considered, and we express no opinion as to, any law other than the Delaware General Corporation Law (including the statutory provisions, and reported judicial decisions interpreting the foregoing).

We hereby consent to be named in the Registration Statement and in the related joint consent solicitation statement/prospectus contained therein as the attorneys who passed upon the legality of the T-Mobile Shares to be