Every iPhone contains a slot for a SIM card. This card is an integrated circuit that links the handset to a user’s account with a service provider, along with the phone number linked to that account. iPhones that run on AT&T will need a SIM card to connect to the phone network, but iPhones running on Sprint or Verizon do not need a SIM card to operate. In theory, SIM cards are interchangeable but there are actually several physical and technical limitations on this ability. Whether you can “unlock” a handset, when you can do so, and how much if anything it will cost you, depends on both your network and your contract. In a surprise exception to this usual practice, iPhone 5 handsets shipped to customers by Verizon are unlocked. This means these handsets will run on AT&T if you insert an AT&T Sim card. Taking advantage of this feature does not override any minimum contract period on a Verizon deal: you must still pay its monthly charge while under contract, even if you use a different network. To avoid this monthly charge, you can cancel your contract, but you may be charged an early termination fee. Networks generally use compatible technologies for 3G and 4G data transmission. This means, for example, that a Verizon iPhone 5 with an AT&T SIM can access AT&T’s high-speed 4G services. Writer Bio
