On Friday, AT&T released a statement that they would now be offering SIM unlocks for iPhones that are no longer under contract. The process of SIM unlocking a phone allows it to use SIM cards from other carriers. This feature is frequently used during international travel to allow the use of mobile service from local carriers. The Next Web detailed the basic steps required by AT&T.
The process is painless and only takes a few minutes in the chat. The only piece of information required by AT&T is the International Mobile Equipment Identity (IMEI) number, which can be found under Settings>General>About on your device.
Once you’ve completed the procedure, Apple pushes the unlock code during the next 72 hours to your email address, so the code comes from the mothership, not from AT&T. Once Apple completes the unlock request, a customer has to back-up and restore and tether the device to iTunes to complete the unlock process.
MacRumors readers shared their experiences on Sunday trying to unlock their out-of-contract iPhones in our discussion thread on the topic. Responses from AT&T service representatives were mixed with some seemingly unaware of the process.

Confirmation email from AT&T
Others had better luck, such as Exegesis48, who was able to get his iPhone 3GS unlocked immediately.
I called AT&T Tech Support and was able to get my iPhone 3GS unlocked no problem. In fact, the representative waited on the line to ensure I received my unlock confirmation email, at which point he told me to backup and restore my phone to receive my unlock. I did this and was able to receive my unlock IMMEDIATELY.
Experiences may have improved over the day. Some early callers were told the process would complete on April 16th, while others were told to simply wait 48-72 hours for the confirmation email.
Top Rated Comments
Tens of millions of iPhones are suddenly unlock eligible & AT&T is getting slammed so no hard to believe. If there call center is 50k strong it's still under staffed today. I hate defending AT&T but give 'em a break in this.
I recently bought 2 iphone 4 for my family, they were second hand, but it very good condition. We are allready on att, and to tell the truth, im totally not satisfied with their services. I was decided to unlock them and use it with sprint. I went online for searching how to do it, first i tried to unlock by att but they could not do it, they said its not possible because the iphone is not on my contract. I went online and searched, i found a great site at www.attiphoneunlocking.com The site seemed reasonable, and they were offering permanent unlocking for kind of phones like mine. My iphone was unlocked in 2 hours. I found the solution for my problem, so if theres anybody with the same situation, its good to know.
--The ability to hold you hostage on their system for two years while you're paying off the phone.
--A premium over what it actually cost them to give you the subsidy.
--An indifference to customer service, since they have you by the short hairs.
--The ability to keep you from putting an international carrier's SIM in the phone when you travel to another country, thereby forcing you to pay their exorbitant international roaming charges.
A subsidized phone on any carrier is like "rent-to-own" furniture. Except that, unlike Aaron Rents, you get penalized if you terminate the contract early, because they don't have a provision for letting you return the equipment.
You hit the nail on the head there. The contract/ETF is how AT&T makes sure they subsidy is covered... and should be the only way they're allowed to do it by law.
However, they use the network lock anyway, saying it's about the subsidy but it's not... it goes much further than that. It's being used to force customers to continue to use AT&T as their carrier. It's anti-competitive and shouldn't be legal... but it is in many countries... for now.
At least AT&T isn't charging $50 to unlock like Rogers is... kudos to them.
Frankly, I don't care about the wait. I care that they don't even meet their service commitment of getting me a code by April 16. If I didn't pay them on time they certainly wouldn't accept me saying "Just wait more, I will get around to paying you when I finish other things"