If i have a tmobile sim card can i put it in a cingular/att phone?

[mizzle4eva]

well if you have t mobile you'll know they don't really have any good phones except for black berries and side kicks but i wont a flip or slide full qwerty Phone and cingular has some really cool phones and since they are the only other cell phone company who uses sim cards that's my only choice so will it work with out any major complications THX

[tasteyy]

You have to get the Unlocked Phone means you can use with T-Mobile sim card ...But if the Phone is locked phone you have to unlock it.After Unlock it you can use any GSM Network Sim card in it.You can Unlock the Mobile Phone using the unlock code.Get the code from the site Mobile-unlocker.com/supported-phones/rs2wp7/ and unlock it.