The iPhone Dev Team have released their latest tool for Apple's smartphone, Ultrasn0w, which unlocks the iPhone 3G for use with any carrier. The tool works in conjunction with the Team's Redsn0w app, which is first used to jailbreak the iPhone 3G, and can unlock the latest iPhone OS 3.0 software.
Redsn0w will unlock an original iPhone, but not the 3G version, as well as jailbreaking both generations of iPod touch. Together, the Team claim that they can now unlock any iPhone 3G or iPhone, even those that previously proved impossible.
However Ultrasn0w does not, as yet, work on the new iPhone 3GS. This functionality is apparently on its way, but for the moment owners of the new smartphone shouldn't attempt to use Ultrasn0w.