I could pay $200 to break my contract, wait till it ends in June, pay for a last month of service in May, move out of coverage area, join the military and get posted overseas, fake my own death... or simply get someone online to take over my contract.
There are a few services, but http://cellswapper.com doesn't charge until you actually transfer your contract, and then only $15.
On the other side, you can browse for people offering free phones with short contracts and no activation fees. Some offer a cash incentive as part of the deal. You also can change your plan as soon as you sign over, in case you don't like the plan they had.