Many network providers lock phones to their network and sell them at low cost. When users buy such phones they need to stay with that network till the contract ends. In this way the network provider increases their potential. Incase a user needs to unlock their phone in the middle of contract they can request their respective network provider. If they deny there are many online unlocking vendors like Prounlocking.com who provide permanent unlock through their remote unlocking service.Once unlcoked teh user can swap to other network in their iPhone.