I had the same problem, found a post on a forum somewhere that said to plug the phone into a Windows 7 computer.. You have to do it on a computer that has mini keis installed... something about the process of the pc "seeing" the phone will resolve the problem.... this worked for me.... As far as AT&T... they have no clue... I have argued with two of their reps that my phone is NOT a 4G device.... which I think is just sad....
Good Luck...
Good Luck...