QuickPWN

QuickPWN is an application for Mac that allows you to unlock and jailbreak your iPhone 3G. By this way you'll be able to access the files, change the theme used by the device and install third party applications. It also supports iPod Touch.

QuickPWN version 3.0 Beta 3 is compatible with the iPhone 3.0 Beta firmware, iPhone 3G 3.0 Beta 3 and iPod Touch 3.0 Beta 3.

If you don't want to unlock the device, but you want to jailbreak it, then you'll have to update the firmware to the version 2.2.1 via iTunes and run QuickPWN to jailbreak it.