For all those who have upgraded to the Iphone firmware v 3.1.2 an Unlock was released yesterday by GeoHot.
Blackra!n RC3, the Jailbreak tool is available at http://blackra1n.com and includes the new Unlock. There are versions available for both PC and MAC.

For those who have already jailbroken their Iphones running v 3.1.2, Blacksn0w can be downloaded via Cydia by adding the source http://blackra1n.com to Cydia.
Enjoy!