T-Mobile paying ETF's with device trade in

Just heard a commercial on the radio saying T-Mobile will be paying ETF's with a device trade in. Was this even announced yet? I know it's been rumored for a couple of weeks or so but this was the first I'd heard about it officially. It makes perfect sense since if you're coming from Sprint or Verizon your device will be useless on T-Mobile's network anyway. Discuss.