So far I've legally unlocked 3 contract-complete AT&T iPhones (I don't think you can legally unlock Sprint or Verizon iPhones, so this is a real AT&T advantage). Time to share my experiences.
- Get your phone's IMEI and Serial Number, but really you need the IMEI.
- Go to AT&T's mobile site and look way down the page to the tiny 'contact' link. Or click on the 'bot helper and say you want to unlock your phone.
- Say you want a technical support chat.
- Fill out the form, you'll be asked for the IMEI and your last four of your SSN (if you forget, just Google it. Amazing that this is proof of identity.)
- You're told it will take a few minutes to get the email and 1-2 days for things to be processed; which doesn't seem to make sense.
AT&T will unlock an iPhone under the following circumstances:
The person requesting the unlock is:
a current AT&T customer or a former AT&T customer who can provide the phone number or account number for the account
All contract obligations, including any term commitment, associated with the device to be unlocked have been fully satisfied; and The iPhone has not been reported lost or stolen.
Current customers will be allowed five (5) unlocks per account, per year, so long as their account is in good standing with no past-due amount or unpaid balance and has been active for at least sixty (60) days. Former customers will be allowed five (5) unlocks per former account so long as they owe AT&T no Early Termination Fee or other unpaid balance.
The 5 unlock limit is interesting, I'm actually closing in on it. It's interesting they'll even process unlocks for former customers.
We have one iPhone 4 a friend gave us (needed repair), I'd like to unlock that one too. It sounds like she could do the unlock so long as she can provide the account number that the phone was purchased with. I'll have to give that a try sometime, I'm curious to know if it will work if I 'restore' that phone to my AppleID.
I really don't understand why AT&T ended its previously infuriating eternal lock program - a lock that applied even to a fully paid off phone . It's so unlike my image of them. It's equally mysterious why Verizon gets away with their eternal lock.
 Currently I have one phone on one Apple ID, and a bunch of phones and computers on another. Apple's ID system is so very broken.  Note, however, even a carrier-locked AT&T phone will work with AT&T resellers such as H2O wireless.
- AT&T Customer Device Unlock Portal - Request
- iPhone: About unlocking: Apple's directions, which are a bit different from AT&T's directions. Apple advises erasing content from the iPhone, AT&T advises doing a "Restore" from iTunes. (Restore, of course, doesn't 'restore from backup', it "restores" the phone to a fresh state. Reminds me of when we used format a: to format a floppy disk and a typo ("c") would wipe your hard drive.)
- Pay-as-you-go voice and SMS service for a contract-free AT&T iPhone with H2O Wireless
I unlocked another iPhone 4, this time using their new web form. This phone had an H2O wireless SIM and was registered to my Mac account, but I was able to unlock it with the prior owner's AT&T number (she still has active account and the number that was previously used with this phone) and the last four of her SS. I can't remember if we needed anything else. It did take several days for the unlock email to arrive.