After offering an unlocked version of the iPhone overseas for some time, Apple has finally begun selling an unlocked version of the GSM iPhone 4 here in the US. Rumors had been building over the last several days that Apple was preparing to add such an item to its inventory system sooner than later, and those rumors came to fruition early Tuesday morning.

The unlocked 16GB iPhone 4 is now available directly from Apple for $649, with the 32GB model going for $749. (Bet you're hankerin' for those subsidized phones again!) Unlocked iPhone 4s are available in both black and white and the device is otherwise the same as the AT&T-locked iPhone 4 that many of us are already familiar with.

Aside from being beneficial for travel—GSM is essentially the world standard when it comes to cell phones and travelers will be able to use the device on other GSM networks outside of the US—an unlocked version of the phone means that users can upgrade without committing to a new contract with AT&T. T-Mobile in the US also offers a GSM network that partially works with the iPhone 4, but those who take unlocked phones over to that network won't be able to use T-Mobile's 3G—the device works with T-Mobile's EDGE only.