https://www.theverge.com/circuitbreaker/2017/10/23/16527536/t-mobile-300-off-iphone-x-deal-trade-in-discount

All the major US carriers are announcing their iPhone X deals, and now T-Mobile is joining the party with an offer that’s pretty similar to what Verizon and Sprint have on tap: trade in your current “qualifying” iPhone, and T-Mobile will give you up to $300 off your iPhone X.

Like Verizon, you’ll have to purchase the iPhone on one of T-Mobile’s installment plans (either the regular “Equipment Installment Plan” or the company’s Jump! On Demand leasing program, which allows for more frequent upgrading, with the trade off of never actually owning your phone).