That's a very tough thing to do, man. Depends what your problem is. If it's something with their service just call or email them and act like you're mad, but respectful.
If you just want to switch to a different service provider to get a new phone, you can ask someone at a store specific to the company (Verizon Store, Sprint Store...) if they will buy out the rest of your contract with Verizon to switch to them. If you don't have much time left on your current contract, they might do it.


I know this thread is over a month old, but it could still really help somebody. Plus, asking a question and not getting a response ever really sucks...