The iPhone Dev Team have released version 2.0.1 of their infamous Pwnage Tool, which can now activate and jailbreak a 3G iPhone. Unfortunately, unlocking the phone for use with another SIM card is still a work-in-progress.
With the first 3G-supporting Pwnage Tool 2.0 released just yesterday, 2.0.1 adds fixes to a number of issues that were stopping many people from successfully "pwning" their phones.
With launch issues sorted, and the applications you've already bought from the App Store reported to play nice alongside their unofficial brethren, there's now no reason not to give it a shot.
PwnageTool 2.0.1 [blog.iphone-dev.org]