Your device supports the following bands
3G Band 900 MHz , 1900 MHz , 2100 MHz GSM Band 850 MHz , 900 MHz , 1800 MHz , 1900 MHz Wireless 802.11 a/b/g/n
T-Mobile bands supported ar GSM1900 (EDGE)
the only way to obtain 4G speeds is to obtain as T-Mobile Sonic (Mobile Hotspot) and connect to the Hotspot by WiFi of your phone.
Otherwise you are limitied to GSM1900 EDGE speeds
As T-Mobile starts building out the LTE network they will also enable 3G band 1900....whihc this device supports.
So it will eventually work as a 4G device with T-Mobile....no time lines of course (no idea, not my area)