If you are looking to unlock your iPhone 3G or 3GS device, and use it on any network, your wait will finally come to an end shortly. George Hotz aka GeoHotz, has announced that he will release the Blacksn0w tool to unlock iPhone 3G and 3GS on baseband 05.11.07 very shortly.
GeoHotz has also created Blackra1n which allows you to unlock iPhone/iPod Touch 3G and 3GS devices.
The Blacksn0w update will let you unlock iPhone and use it on any other carrier. George Hotz has posted a video of the first unlocked iPhone 3GS phone baseband 05.11.07.
According to the video, Blacksn0w will most likely be released on November 4th 2009, so hang on till then and you can achieve carrier freedom with your phone :-).