Today Apple announce iTunes 9 along with iPhone OS 3.1 (Build 7C144). As DevTeam said, iPhone users who wants to unlock their iPhones with Ultrasn0w should not update their iPhone to 3.1 and have to wait for new version of Redsn0w and PwnageTool.

Below you can find direct download link for iPhone OS 3.1

iPhone 2G – iPhone1,1_3.1_7C144_Restore.ipsw
iPhone 3G – iPhone1,2_3.1_7C144_Restore.ipsw
iPhone 3GS – iPhone2,1_3.1_7C144_Restore.ipsw