The Dev Team has updated redsn0w previously used to jailbreak the iPod Touch 2G to jailbreak the iPhone 3GS! The jailbreaks works on Windows, OSX, and Linux.
Last night we released updated versions of our redsn0w jailbreak and ultrasn0w carrier unlock. These versions are now compatible with the iPhone 3GS running at 3.0. Welcome aboard, 3GS owners! (The tools of course remain compatible with all of the other platforms too.) Also last night, saurik released 3GS-compatible versions of MobileSubstrate and WinterBoard, components that enable many different add-ons and themes.
How to get the goods:
* The redsn0w torrent seeds are all here. Any direct mirroring help would also be appreciated.
* The updates to ultrasn0w, MobileSubstrate, and WinterBoard are all handled directly through Cydia (after you’ve jailbroken!)
* The Cydia repo for ultrasn0w is http://repo666.ultrasn0w.com (that last o in ultrasn0w is the number 0!)
[Source - Dev Team]