You can use any handset on our network you want. We don’t prohibit it, or even police it… AT&T Mobility President Ralph de la Vega

GSM ,AT&T network technology used by more than 80 percent of the phones in the world wide.The GSM phones store all the data info on a SIM card ( subscriber identity module ) so you can remove the data card (SIM) and place it into another unlocked cell phone.in any network you like as long as it has GSM technology.

Got an T-mobile phone you want to use with AT T? As long as they are a GSM-compatible phone, and you have really unlocked it,it will work.
You can use your unlocked phone in England,Canada,or yes even China.

ATT has always has had this open,unlocked policy,but just never has made it known to the public like it is doing now.In fact ATT is the one carrier that is willing to be open ,er unlocked that is) about their cell services and unlock cellphones.

Thats why they will be the front runner in unlocked cell services