Before the release of iPhone OS 3.1, the legendary iPhone Dev-Team had warned all the iPhone 3GS and 3G users who have jailbroken or unlocked their iPhone to stay away from this iPhone firmware update.
Now once again they have updated their blog and have added the best part for the jailbreak community. Now the Dev-Team blog says that we are working on PwnageTool to jailbreak iPhone OS 3.1:
We’re currently working on PwnageTool for 3.1, and will be sure to let you know when it’s available!
Remember, each upcoming firmware update not only update your iPhone OS but also its Baseband (Modem firmware). Once the iPhone Baseband is updated, it’s almost impossible to unlock your iPhone then.
There comes the PwnageTool to handle the Baseband. PwnageTool allows iPhone users to update to iPhone OS 3.1 while preserving the Baseband (Without updating Baseband). Once you remain on the same Baseband, it means you can use UltraSn0w to Unlock your iPhone.
via: Dev-Team Blog