can i put a tmobile sim card in a att or cingular phone and be able to use it?

Answer 1

yes and no.

Yes, your sim chip will work in a Cingular phone.

No, it wont work until the phone is unlocked. The phone is locked to Cingular/att service and placing your chip in there will ask for a subsidy code or simply state "incorrect sim". Phone unlocks can be done through many dealers, or online sometimes. Do a yahoo search for the model phone you are looking at, plus "unlock" and youll likely find your phone for sale already unlocked, or a company that will unlock it for a fee.

Answer 2

if the at&t (cingular ) phone is unlocked then yes and if the phone is not unlocked then no ,but if it is locked then it can be unlocked