Cingular and AT&T

[NorCalJosh]

pop open your phone, pop the battery out, theres a tiny card in the back. thats the sim chip. each companies phone is locked so that only that particular companies sim chips work with it. to maintain your plan, you have to have your ATT sim chip. and your ATT sim chip wont work in current cingular phones, since they are locked to only accept cingular chips.