The unofficial iPhone dev team have confirmed moments ago that they have completed an iPhone 3G unlock and are currently packaging a user-friendly application with the simplicity that you see in other applications from the team like QuickPwn.
The update will be released on New Years Eve and will require a jailbroken iPhone and 2.11.07 baseband or earlier. Jailbreaking is a method of unofficially hacking the device and allowing it to run 3rd party applications not available on Apple's official AppStore. The latest iPhone 2.2 software updates the baseband beyond 2.11.07 and it is recommended that if you want a 3G unlock that you do not update to 2.2 using iTunes alone.
It has taken the team just over 6 months to hack the iPhone 3G and has been the main focus of their efforts.
The dev team have also commented on Apple's OSX update which has blocked jailbreaking, "We believe this behavior is due to a kernel bug not a specific countermeasure by Apple", some workarounds have been suggested.