In Short

T-Mobile is the multi-national carrier subsidiary of Deutsche Telekom AG that serves Windows Phone owners, among others, in Europe and the United States.

T-Mobile US, Inc. is the American operating entity of T-Mobile International AG. The fourth-largest carrier in America, T-Mobile U.S. is headquartered in Bellevue, Washington. As of August 2014, T-Mobile is the largest prepaid provider in the United States with 15.64 million prepaid subscribers on the network. T-Mobile US has over 50 million total subscribers.

T-Mobile has carried Windows Phone devices since the launch of the operating system in late 2010. The HTC HD7, running Windows Phone 7, was one of the first Windows Phones available and was sold by T-Mobile. T-Mobile has carried phones like the HTC Radar, Nokia Lumia 710, Nokia Lumia 521, the Nokia Lumia 925 and recently the Lumia 635.