As rumored for a while now, Apple has started selling an unlocked version of the GSM iPhone 4 in the US. After offering an unlocked version of the iPhone overseas, the move was inevitable, though it took quite a while.
The unlocked 16GB iPhone 4 is available directly from Apple for $650 while the 32GB model goes for $750. Unlocked iPhone 4s are available in both black and white at the Apple Store.
An unlocked version of the GSM phone means that users can buy it without signing a new contract with AT&T. Unfortunately, the T-Mobile GSM network in the US only partially works with the unlocked iPhone 4: T-Mobile's EDGE is compatbile but T-Mobile's 3G is not. In other words, this is really meant for Americans who travel internationally, since GSM is used by most carriers worldwide.
I'm not sure this is worth purchasing. Although the iPhone 4 is not best phone available right now, in my opinion of course, it's also going to be replaced very soon. While we don't know when the iPhone 5 will arrive, we do know it's coming soon.
The iPhone 5 was largely expected to arrive this month, given the iPhone's history. The first iPhone was released on June 29, 2007. The iPhone 3G was introduced on June 9, 2008. The iPhone 3GS was announced on June 8, 2009 and arrived on June 19, 2009 in the first countries. The iPhone 4 was announced on June 7, 2010 and released on June 24, 2010.
Since the iPhone 5 was delayed, recent rumors have suggested production for the device will start in either July or September, but both expect it to arrive in time for this holiday season. If you are absolutely set on buying an iPhone, then you should wait. The iPhone 4 was a great phone when it came out, but now it's no longer the cream of the crop, so you should hold off until the iPhone 5 is out.