As far as I know the AT&T model will work on the T-mobile network, but you have to unlock it first. Once unlocked, it will detect the T-Mobile sim, and will download the correct software update and your in business. I bought a Rogers of Canada model, unlocked it and I am running on the T-mobile 4G network.
Originally Posted by meltbox360
I sold my black unlocked model I was using on T-Mobile to a guy who was using it on AT&T USA and once he put in his sim card, the phone detected it, download the AT&T software update and he was on they're 4G network. From what I have read in most of the forums, the z10 100-3 GSM model is the one that most of the North American GSM carriers will be using and thats the information I used before I bought mine..