Here is a link to a good article on the recent exception that was created to the DMCA concerning unlocking phones. Carriers Split Over Cell-Phone Unlocking
Basically the carriers don't know how they will handle it. It seems that T-Mobile has the friendliest stance and Sprint, being the pricks they are, refuse to unlock phones saying that they are not doing it because it is best for the customer and their experience on their system. It sounds like Cingular is somewhere in between. I have been both a Sprint customer and now use T-Mobile. I have never had any issues with TMO but Sprint was a nightmare. Anyway have a read and formulate your own opinion.