You can Use this phone to replace your AT&T Or T mobile Phone just switch the sim Card Prepaid OR Postpaid;Bluetooth 2.0+EDR;Unlocked cell phones are compatible with GSM carriers like AT&T and T-Mobile as well as with GSM SIM cards (e.g. H20, Straigh Talk, and select prepaid carriers). Unlocked cell;Operates on dual-band GSM 850/1900MHz wireless networks;PHONE TAKES A STANDARD SIZE SIM CARD