I have a 1520.3 and had it on T-Mo for months. It got every data speed without issue and internet sharing just worked right out of the box.
Any 1520 means giving up WiFi calling, so if that is important to you in any way don't stray off of T-Mo branded hardware.
Personally, when shopping devices I found RM-938 (1520.3) superior to the AT&T version and available at a lesser price. Why not get more for less?
- Built in Qi charging without a special case required
- 32GB internal storage automatic
- Factory Unlocked and with all the right frequencies to make it portable and compatible with any GSM network in North America