Next week my year long contract with a phone company expires and I am writing to them to state that I don't want to renew the contract. I've decided to buy a new phone and return to pay-as-you-go. But someone wants to buy my contract phone. Is it mine to sell? And how do I ensure that I won't be charged for calls the new owner makes on my old phone? What happens to a phone's viability/connectivity once the contract has ended?