I was looking at Sony's developer white pages to get more detailed information on the device's specs and features. It looks like there will be multiple versions of each of these devices and not all versions will work with our 4G network (Band IV 1700/2100 MHz). The versions you listed (C6602, C6502, C6506) are all stated to support Band IV so they should work on T-Mobile's network.
Hope this helps!
To continue the thread, it looks like the ZL supports LTE
UMTS HSPA+ 850, 900, 1700, 1900, 2100 GSM GPRS/EDGE 850, 900, 1800, 1900 LTE Band I, Band II, Band IV, Band V and Band XVII
There will be a TMO branded Z coming soon too that will also support LTE.