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.