The time has come for Mac users to begin jailbreaking their OS 3.1.2 devices.  According to the iPhone Dev Team, PwnageTool 3.1.4 for the Mac now supports OS 3.1.2 and can be used on the iPhone 2G/3G/3GS and iPod Touch 1G/2G.  At the moment the software does NOT support the iPod Touch 3G, but a later update will address that device. Now for the important notes:

This release allows your baseband to remain unlocked at 3.1.2, but it does not unlock a new baseband put there by restoring to official 3.1.x. It is super important that people who need the unlock to understand they can keep it only by starting at 3.0 (or earlier) and updating solely to custom IPSWs that don’t update the baseband. For those who have been onboard the “unlock train”, simply install ultrasn0w via Cydia once you’ve restored to your custom IPSW. Don’t forget to turn off the “3G” setting in Settings->General->Network if you use T-Mobile in the U.S.A.

[Via iPhone Dev Blog]