As Clinton's campaign strategist James Carville used to say: "It's the economy, stupid."
Take a good look around: Companies are bleeding money and we, the people, are bailing them out left-and-right. I think T-mobile is smart enough to acknowledge (albeit quietly) that customers' loyalty is far more important than the marginal-profit they make from phones that are subsidized by the phone companies in the first place. If they get a customer to sign up for two years: That's where their real money comes from! And if the customer is happy he/she will sign up for another two-year contract when a new phone arrives. And so on.