What is a SIM card used for? A SIM card, or a subscriber identity module/subscriber identification module, is a tiny memory card that contains unique information and is linked to a particular network ...
In the US, the iPhone 4S comes on AT&T, Sprint, and Verizon, but one major carrier is noticeably absent: T-Mobile. But a method has surfaced to unlock the iPhone 4S that allows it to be used on the ...