The iPhone Dev Team have announced that they are delaying the release of the updated ultrasn0w iPhone 3GS jailbreaking and unlocking tool. In a post on the Team's blog, they detail the nature of the exploit used to jailbreak (and then unlock) the 3GS, a loophole which Apple could readily close once it was made public.
"Here’s the critical point, the reason why we’re delaying our version of the jailbreak: Once the jailbreak is out, Apple will fix the iBoot-family bug we use to accomplish it. They will simply stop signing the old iBoots and only sign the fixed ones. If you bought your phone after Apple has done this, there’s nothing you can do…the jailbreak isn’t going to work for you." iPhone Dev Team blog
According to the Team, the exploit depends on an iBoot-family bug, which can only be addressed if users have a signed iBoot-family img3 from their own device. This contains their ECID, a unique chip identifier different on each iPhone 3GS. If Apple discover the loophole, they could update the smartphone and refuse to sign any old iBoots; then those users would not be able to jailbreak or unlock their handsets.
The Dev Team are counting on an imminent iPhone OS 3.01 update which addresses some of the platforms more buggier aspects, and are waiting until then to see the state of play. They've given no indication of when the iPhone 3GS jailbreak and unlock option might be released, a situation that's prompting no small amount of revolt in their comments.