This tutorial demos how to factory unlock your off contact AT&T iPhone 4/4S to another GSM carrier such as T-Mobile. Factory Unlocks ensure your iPhone will still be unlocked when you update firmware. It lasts forever! Works with iOS 6/5/ ect.
Any GSM carriers will work, T-Mobile is an example
To complete the unlock, simply
1. Open iTunes on your Mac or PC and verify that you have Internet connectivity.
2. Ensure a SIM card is inserted into your iPhone.
3. Connect your…