9to5Mac reports that Apple has changed the requirements for buying an off-contract iPhone in the USA. US buyers have been able to purchase off-contract iPhones at "list price" for quite some time, but they still had to present proof of an AT&T plan at the time of purchase. That requirement has been removed.
For twenty brief, shining minutes, this sounded like the iPhone was being offered unlocked by Apple, which would have been truly huge news -- if you wanted to use the iPhone on another GSM carrier (meaning T-Mobile, in the States), you could have done it without jumping through any extra hoops. According to both 9to5Mac and Engadget, however, it appears those initial reports were incorrect: the iPhone is still locked to AT&T, though according to one source (supposedly an Apple retail employee), "it takes like 2 minutes to unlock them."
iPhones have been available unlocked in other countries for some time now, but the US is definitely the iPhone's biggest market. Having the iPhone available for sale unlocked, officially, via Apple, would have been a huge deal. But that day, unfortunately, doesn't seem to have arrived quite yet.