One of the major obstacles for potential iPhone buyers is that the iPhone is offered exclusively via select carriers. Even if users are willing to switch carriers, they may not be willing to eat the often multi-hundred dollar early-termination fee that they would incur.
Several websites are now available to help users avoid various cell carrier fees. Cellswapper.com and Celltradeusa.com both are geared towards helping users seeking to end their contracts early avoid early termination fees, while helping new customers avoid activation fees.
Both sites work on a similar principle in that service providers will typically allow the transfer of contracts without termination or activation fees. The sites therefore act as a meeting place for users to find each other.
Note that the service is not without any cost, as the sites do charge a fee for matchmaking, however the end result should be considerably less than termination and activation fees.
MacRumors.com does NOT have any kind of business relationship with either of the websites aforementioned.