The iPhone is a quad-band cellular phone based on the Global Systems for Mobile Communications (GSM) network. Phones operating using the GSM standard have Subscriber Identity Modules (SIM) cards. SIM cards allow cellular service providers to identify cellular subscribers using their network. SIM cards are removable and a cellular subscriber can transfer a SIM card between phones. The iPhone is normally sold with a carrier lock that prevents using the phone with another cellular service provider’s SIM card. You can tell if your iPhone is locked, by inserting another SIM card into your iPhone. Writer Bio
