Celltrade is a company that helps you to get out of your current phone contract. That way you can sign up with cingular to get the new iPhone.
It sounds like you basically sell your contract to another person. Celltrade just plays middle man. It costs $19.99 but hey that’s cheaper than paying $250 to buy out your contract and then another $599 for the iPhone.
Or if you want to get out for free there are some other alternatives… heh