As early as last week, my sources in the Apple food chain were hinting at some sort of way for Apple Stores to unlock AT&T iPhone 4s – different than the unlocked models that Apple Stores started selling on June 13th. Now, a trusty retail source hit us up with the above note from an Apple Retail Project Manager, saying that Apple Stores can now unlock the AT&T version of the iPhone.

Basically, if a respective Apple Store is running low of the unlocked GSM SKUs of iPhone 4, they can pull out an AT&T SKU and, at checkout, the system can choose to unlock it. Obviously, this will only work if the customer pops out the full $650 for the 16 gigger or $749 for the 32 GB monster.

Apple has previously been able to sell contract-free iPhones for those aforementioned mega prices – but those phones were still strapped to AT&T. With this new route, people can run off to international carriers or cut up their SIM to work with T-Mobile in the U.S. As we previously reported, T-Mobile is now carrying over a million iPhone users in the United States.