Conventional wisdom has it that the tools for JBing the 3Gs will be out AFTER Apple releases the 3.0.1 firmware update. How soon this will be is anyone guess.
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iPhone 3G[S]; FW-3.1
iphone 2G (now an 'iTouch with Skype capabilities)
MBP-2.33GHz/3GB/15-inch
It's a way to break away from apple's software and open up whole new possibilies to customize your phone. It has it's own "unofficial" apps and some are alot better than the regular ones. For example: The 3g jailbreak had an app that could take video.