Geohot first released the 3GS Jailbreak solution and the Dev Team, who initially planned on releasing their version of the Jailbreak after Apple released iPhone 3.1 firmware had no other choice but to release it immediately! Dev Team’s redsn0w handles the jailbreak for your iPhone 3GS more like the 3G and 2G variations.

Download redsn0w using the following links :
redsn0w for Mac OS X
redsn0w for Windows
redsn0w for Linux (introducing!)
Click here for a simple and quick guide to get you up and running with this revolutionary iPhone 3GS jailbreak. Don’t hesitate …

For a change, I published 3 videos which definitely enables a total noob to unlock his/her iPhone without much difficulty. Latest Firmware via iTunes (2.2), QuickPwn (Jailbreak) and yellowsn0w via Cydia/installer (Unlock) hold the three key steps for a successful unlock.
Before proceeding further, make sure you are equipped with the following :
1) Strictly iPhone 3G Updated to 2.2 firmware via iTunes (2G iPhones have a different process – BootNeuter from Cydia).
2) Intel Mac (10.5.6 s/w update) or Windows machine. [Mac users, make sure DFU mode is enabled (10.5.6 s.w update …

iPhone 3G Unlock (codename : yellowsn0w) is finally ready for general consumption with an anticipated release date of December 25 ~ 31 (Christmas — > New Year’s eve!). It is currently undergoing idiot proof GUI packaging for the total noobs! However, those users who accidentally upgraded to 2.2 firmware from iTunes have no other choice but to resort to x-Sim solutions or a possible baseband downgrade from 2.28 to 2.11 (hopefully).
Great job iPhone Dev Team, you really rock the iPhone world and Apple likes it too, not sure about ATT …