T-Mobile's just-announced "JUMP"—Just Upgrade My Phone—plan that lets its customers get a new device for just $10 a month would finally get people buying iPhones on the network—if price had anything to do with T-Mobile's problems. Unlike other carriers, which don't let users upgrade their phones until the end (or very close to the end) of their two-year contracts without paying the full retail price (a lot!) for a brand new phone, T-Mobile will now charge an extra $10 a month, which yes, is a good deal. But, it turns out deals aren't the number-one thing people care about when picking their carriers.
If you work out all the math, T-Mobile's upgrade scheme beats the competition, plus you don't feel locked in by some arbitrary carrier demand, which has its mental benefits. T-Mobile charges $99 for a new iPhone up-front and spreads the rest of the cost in $20 installments over a two-year period. Now, if you choose to swap phones at say, month 12, you ditch those $20 installments for $10 ones and then can get a brand new phone at the cheaper price. Plus, T-Mobile doesn't build the full price of a smartphone into the plan.
It's cheaper, at least to buy the physical device. Here's the math breakdown: At 12 months on Verizon, you would pay $200 for the original iPhone plus another $650 for the new phone, all the while subsidizing that $200 iPhone. So it's at least $850 just for the phone part, with more expensive plans for the next 12 months. At 12 months on T-Mobile you pay $99 for the phone up front, plus $20 per month, which adds up to $339 for the phone for a year. The new phone then costs $99, plus $30 a month after that ($10 for the upgrade, and $20 a month for the monthly payment). In total, that's $798 for the phone. And, all along, your data, talk, and text plans should cost less, though that's up for debate. At the very least it should feel freer than being locked in for two years.