How to Unlock iPhone 4 on iOS 6.1.2 With Baseband 04.12.05

Unlocking an iPhone 4 with baseband 04.12.05 is not possible through software tools like Ultrasn0w, regardless of whether the device is jailbroken. For this specific modem firmware, the most reliable method is to request an official IMEI unlock from the carrier the phone is currently locked to. Many carriers will unlock older devices like the iPhone 4 for free if the contract has been fulfilled. Alternatively, you can use a reputable third-party IMEI unlocking service, though these often require a fee.