Well I think it's most likely dependent on geographic region. Like dr3wster said the Moto X is listed with bands 2/4/5/17. AT&T operates band 2 (1900MHz) nationwide. Band 4 (1700MHz d/e) which it acquired from Leap Wireless, so I'm guessing areas that Leap served before AT&T took over the spectrum. They have 1700MHz d/e deployed nationwide and in Puerto Rico, so it's a bit difficult to say if you'll actually get LTE on T-Mobile with the AT&T Moto X. I know Metro PCS LTE works on 1700MHz (d) so it'll work with the AT&T Moto X. But it supports T-Mobile's d/e 1700MHz bands so I don't really see why not. Band 5 is the 850MHz. Band 17 (700MHz b/c) is mainly Puerto Rico and US Virgin Islands. I'm ordering one to unlock for use on Metro PCS.