You can't just 'cancel a contract'. The whole point is that you have agreed to pay a certain amount each month for the given period.
So - if you attempt to stop paying, you keep the phone but they are entitled to most (or indeed all) of the payments up until the end of the contract - the precise terms will be in the small print that accompanied the contract.
The only way out is if the phone company breaks its side of the contract (say by increasing the price) - that will then give you a window during in which you can cancel for free.



