Some cellular providers require iPhone owners to bring their device into a store for unlocking and others send an unlock procedure to the customer. As of February 2015, United States wireless providers have voluntarily agreed to unlock a customer's phone upon his request if he meets the conditions.
Paid-in-full financed devices and contract phones with completed contracts are eligible for unlocking. Customers who pay an early termination fee are also eligible to unlock the phone. Carriers require customers to pay any late bills in full before unlocking the device. Prepaid cellular phones are eligible for unlocking after one year's service in most cases. Deployed military personnel, in good standing with the carrier, are eligible for unlocking phones.
The agreement requires the company to respond within two days of a request for unlocking a device, either with the instructions to unlock the phone or an explanation as to why they are keeping the it locked.
Unlocking a phone does not guarantee it works on all carrier networks. If a cellular provider uses a different frequency than the original provider, the phone is unable to access that network. Customers transferring an unlocked phone to a new network sometimes lose services. After the transfer, some devices continue to provide voice service but do not offer data services.