"Unlocked Phones" This term is used loosely in the cellular phone industry and more recently after the white house decided it was legal to "unlock your phones" Unlocking is a Term that allows a person with a GSM (Global Service for Mobile) to use their phone on another carrier SIM (Subscriber Identity Module) Cards from one carrier say for example AT&T Can take their at&t sim card and put it into a t-mobile SIM UNLOCKED phone Usually at&t sim cards cannot be used in most older US Cellular, Sprint, Verizon phones as they either were not SIM unlocked or were CDMA a common misconception about phones and SIM cards is if a phone has a sim card slot then it will just work NOT TRUE the radios in your phone operate on certain radio frequencies and if a phone doesnt operate on that frequency band even if its unlocked it will not work