How to unlock iPhone 4?

Unlocking an iPhone 4 can be done through a few different methods depending on your firmware and baseband version. The most permanent and recommended method is a factory unlock, which is typically requested through the original carrier the device was locked to. Once the carrier approves the unlock, you simply connect the iPhone to iTunes to complete the process. Historically, software unlocks like ultrasn0w were used for certain older baseband versions on jailbroken devices, and hardware solutions like Gevey SIM interposers were also popular. However, most users today should contact their carrier or use a reputable third-party IMEI unlock service for a permanent factory unlock.