i read this on the dev teams blog and its pretty much saying you will not be able to unlcok the 3gs on 3.1
NOTE #1: the carrier sim unlock is a different story. Jailbreaking and unlocking have two different security mechanisms, and if you update your 3GS (or 3G) to 3.1, you will lose your carrier unlock, possibly forever. Even if you downgrade from 3.1 to 3.0, you will have lost your carrier unlock. So if you think you?ll ever want to carrier unlock your 3G or 3GS (or maybe give it away or resell it later as an unlockable iPhone), then please stay clear of all official Apple IPSWs. You?ll soon be able to create custom 3.1 IPSWs using PwnageTool that let you pre-hack your 3.1 update in a way that preserves the carrier unlock.
NOTE #1: the carrier sim unlock is a different story. Jailbreaking and unlocking have two different security mechanisms, and if you update your 3GS (or 3G) to 3.1, you will lose your carrier unlock, possibly forever. Even if you downgrade from 3.1 to 3.0, you will have lost your carrier unlock. So if you think you?ll ever want to carrier unlock your 3G or 3GS (or maybe give it away or resell it later as an unlockable iPhone), then please stay clear of all official Apple IPSWs. You?ll soon be able to create custom 3.1 IPSWs using PwnageTool that let you pre-hack your 3.1 update in a way that preserves the carrier unlock.