T-Mobile is a multinational mobile phone operator. It is a subsidiary of Deutsche Telekom and belongs to the Freemove alliance. T-Mobile operates GSM networks in Western Europe and the United States and participates in network operations in Eastern Europe and Southeast Asia through financial means.

2011-03-21 AT&T, the second largest mobile operator in the United States, announced that it will buy T-Mobile, the U.S. unit of Deutsche Telekom, for $39 billion in cash and stock. The deal has been approved by the boards of directors of both companies but faces regulatory scrutiny. After the entire deal closes, AT&T will pay about $25 billion in cash to Deutsche Telekom and 8 percent of its own equity. A representative of Deutsche Telekom will also join AT&T's board of directors. AT&T's acquisition of T-Mobile will give it more access to wireless communications as consumers increasingly use their phones to surf the Web, watch video and download data. The deal will increase call capacity in some places by 30 percent. The acquisition will also give AT&T 129 million subscribers, or about 43 percent of the U.S. mobile market. Verizon has 100 million subscribers in the United States, and Sprint has 50 million.

In February 2022, T-Mobile US and its parent company Deutsche Telekom (DT) launched T-IoT, which aims to simplify the Internet of Things.

On June 22, 2022, PCMag released its annual Mobile Network Comparison, which named T-Mobile the "best" carrier in the United States for connection speed and reliability.

On July 2, 2022, a T-Mobile spokesperson confirmed that the official shutdown of the remaining LTE towers of U.S. wireless carrier Sprint has begun. T-Mobile has retired Sprint's wireless spectrum for its 3G and LTE networks to accelerate bandwidth growth and accelerate the coverage of its nationwide 5G network.