CMO Mike Sievert explains the ETF program. T-Mobile will pay up $350 of ETFs per line, on up to five lines. Additionally, when you trade in a phone, you'll get up to $300 as a trade-in credit. All told, you could get up to $650 for switching.
T-Mobile is also offering all of its top smartphones for zero dollars down for qualified customers, meaning those with good credit. You'll still have to make monthly payments on the new device, per T-Mobile's payment plans.