Hackers have been trying to unlock the iPhone since day 1 and there have been a couple of ways people have come up with, including messing with the internals and creating a new SIM card, but these have required some skill and effort that your average user will most likely not even try. However, today marks the day that the hackers have done it with a software unlock tool that has been verified by Engadget to work on the iPhone with T-Mobile USA.
The process seems pretty straightforward and was created by the guys at iPhoneSimFree.com. The commercial launch of the service has not yet gone live, but I hope they do it soon before Apple or AT&T are able to shut them down. They apparently even were able to perform the unlock after a full restore so it should be firmware update-proof, until Apple figures out what they did and tries to shut down the functionality. As a T-Mobile customer who had to add AT&T to get the iPhone I plan to put my T-Mobile SIM in my iPhone so I can use it as my daily phone and maybe keep the AT&T service for the HSDPA functionality I get with my HTC TyTN, but I'll have to see if that is cost effective. If not, I may just pay the US$175 early termination fee and stick with T-Mobile.
I personally think this could result in more sales of the iPhone for Apple since there are some people that are very happy with T-Mobile and would love to have an iPhone. This may also boost international sales of the iPhone.