I agree that some hackers may find this challenge interesting and that this may actually be a way of feeling some achievement in life, but really, what's exactly the point of unlocking the iPhone?
VitaminCM makes a good point about it:
It only works on GSM networks and the last time I looked (U.S. only) there are two AT&T and T-Mobile. So what have you achieved? Well, sure, you could cancel your AT&T contract and move over to T-Mobile. You still have to buy out of your AT&T contract (175$ cancellation fee) and you still have to pay for a new contract with T-Mobile ($29 - $79 a month + Voice Plan).
Your warranty on that $500 - $600 phone is now voided. (Good luck when you have a problem.)
Apple already got paid when you bought the phone. AT&T got paid when you signed the contract. You pay cancellation penalty to AT&T and they don’t have to provide the service.(Get money, don’t provide service, sounds pretty good.) T-Mobile gets paid.