I'm using my T-Mobile Note 3 with ATT right now. If I remember correctly I just popped in the SIM and it worked. This is after I set it up with a T-Mobile card, though, and I may have unlocked before using the ATT card.
Now I have it rooted too, everything is fine.
EDIT: sorry I forgot to mention I also changed the APN settings after putting in the ATT card. I think you have to do that too. Bookmonke in his better response below has the link with the info.
NOW FOR A HIJACK:
I want Google Wallet to work, so I think I need to upgrade to KitKat.
Any suggestions as to which ROM to use on this phone that is both KitKat and will work best with ATT?
Also I guess I will have to install TWRP or Clockwork, and thus 'trip Knox' whatever that means. Should I care? I'm not going to return the phone at this point.
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