According to MuscleNerd, the “Spirit” jailbreak could also allow users of the latest iPhone 3GS models, which come with updated Boot ROM to unlock their iPhone (i.e. baseband 05.12.01 that comes bundled with iPhone OS 3.1.3) to use it with any carrier.
“the "Spirit" JB will (also) work on 3.1.3 when released.”
“3GS owners benefit from "Spirit" even more than 3G (since 3G is forever JB-able). Also, both 3G/3GS can use next carrier unlock.”
However, he still hasn’t provided a release date on when the software tools to jailbreak and unlock iPhone will be released, which many users are eagerly waiting for.
It is still not clear if Dev Team and Geohot who had announced untethered jailbreak are waiting for Apple to release iPhone OS 3.2 for iPhone and iPod Touch or working hard to get their tools ready.
Update:AppleInsider, MuscleNerd’s Twitter page]