
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.
PwnageTool WILL work for Original iPhone (1st Generation), the iPhone 3G and iPhone 3G(S) and the iPod touch (1st Generation and 2nd Generation) but NOT the iPod touch 3rd generation.
If you are using a iPhone 3G or iPhone 3G(S) with ultrasn0w and rely on ultrasn0w to obtain cellular service then you should only update your device with an .ipsw that is made with the new PwnageTool. There are no second chances with this. You need to remember that PwnageTool will provide an upgrade path to newer versions of the iPhone software in the future.
Download PwnageTool from Dev Team Blog