There are a lot of smartphone trade-in programs from both retailers and carriers, and to be frank, they suck. In just about every situation you can get more for your current gadgets by selling them yourself on secondary markets like Craigslist, eBay, or Swappa. The only reason to sell gadgets to carriers (or any retailer) is the convenience factor. But T-Mobile is positioning itself as the self-styled people's champion of smartphone trade-ins, or at the very least, the best option among its competitors.
The state of North American cellular contract plans might be something that makes Europeans shake their heads in disbelief, but when it comes to phone pricing, Americans have always had it pretty good. Hand over your soul for two years, get Phone X for free (after MIR). Well, it looks like AT&T doesn't think that's the best way to go. No, that doesn't mean cheaper tariffs; don't be silly. Instead, it means more expensive phones, of course!