How to Unlock Your Out of Contract AT&T iPhone
Submitted by Bob Bhatnagar on
AT&T has started to unlock iPhones for customers who have completed their contract obligations. The process is as simple as contacting AT&T customer support and requesting the unlock on your device. Of course, your account must be in good standing (ie. paid up to date) for AT&T to provide the service.

Once your iPhone is unlocked, you are free to install any replacement micro-SIM card from another compatible GSM carrier. This means you can use your iPhone overseas or with another US carrier such as T-Mobile without resorting to any workarounds or jailbreak unlocking methods.