T-Mobile

In the US, AT&T as well as T-Mobile phones use GSM – and most of the rest of the world uses GSM as well. CDMA in the US is Verizon, Sprint and US Cellular. You need to read up on the subject.

The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets.

Of the two, GSM is more widely used around the globe, with availability in more than 200 countries. While CDMA is used widely in the U.S. , it is less common elsewhere — most estimates pin the portion of global wireless networks using CDMA at less than 20 percent. The Verizon network is a CDMA wireless network.