If you are on a contract, and you decide to terminate service with T-Mobile, then T-Mobile will charge you a early termination fee on top of your monthly plan fees. You will get a one big bill in the mail with the total amount due. As far as making payments you can ask T-Mobile on how they handle this. I do know if you plan on making payments this will definitely affect your credit history and T-Mobile will probably report your payments to the credit agencies.