Why was T-Mobile USA finally able to reach an iPhone deal? Because it's ending phone subsidies next year. In a radical move, the struggling low-end carrier says all phones it sells will soon have to be paid for in full, up-front or via installments. With the iPhone 5 (AAPL) selling for $649-$849 unsubsidized, its sales stand to be disproportionately affected. T-Mobile's move will hurt business with customers who demand high-end hardware for $200 or less, but will also allow it to shift entirely to its cheap Value Plans.