Key Features: Quad-core Snapdragon 800 2.2GHz processor; 2GB RAM; 20.7 MP camera; Full-HD 5-inch screen; 3000mhA battery; 16GB on board storage; microSD slot

Frequencies:
Sony Xperia Z1 Honami, Sony Xperia Z1 C6902/L39h, Sony Xperia Z1 C6903, Sony Xperia Z1 C6906, Sony Xperia Z1 C6943

GENERAL 2G Network GSM 850 / 900 / 1800 / 1900 - all versions

3G Network HSDPA 850 / 900 / 1700 / 1900 / 2100 - all versions

4G Network LTE 800 / 850 / 900 / 1700 / 1800 / 1900 / 2100 / 2600 - C6903

                  LTE 700 / 850 / 900/ 1700 / 1900 / 2100 / 2600 - C6906

                  LTE 800 / 850 / 900/ 1700 / 1800 / 1900 / 2100 / 2600 - C6943

T-mobile uses for 4G: 1700/2100

AT&T uses for 4G: 700Mhz, 1700Mhz and 2100Mhz


That's mean that  Model C6903 will work with 4G T-mobile, and them who wants get 4G at AT&T should wait for model C6906