Iphone Cake

SIM unlocking
• United States
Most iPhones were and are still sold with a SIM lock, which restricts the use of the phone to one particular carrier, a common practice with subsidized GSM phones. Unlike most GSM phones however, the phone cannot be officially unlocked by entering a code. The locked/unlocked state is maintained on Apple's servers per IMEI and is set when the iPhone is activated.
While the iPhone was initially sold in the US only on the AT&T network with a SIM lock in place, various hackers have found methods to "unlock" the phone from a specific network. Although AT&T and Verizon are the only authorized iPhone carriers in the United States, unlocked iPhones can be used with other carriers after unlocking. More than a quarter of the original iPhones sold in the United States were not registered with AT&T. Apple speculates that they were likely shipped overseas and unlocked, a lucrative market before the iPhone 3G's worldwide release. iPhones are unlocked by users who wish to use networks other than AT&T's.