The U.S. branch of T-Mobile is running a new "Buy One Get One" promotion in which people buying an iPhone can get up to $700 off a second, as long as they meet the right criteria.
Customers interested in the deal must be switching a number to T-Mobile, and trade in one of a series of eligible Apple, LG, or Samsung phones. In the case of iPhones, options extend as far back as 2013's iPhone 5s.
After buying the two new iPhones, customers must complete a rebate form within the next 30 days. Once T-Mobile receives the trade-in, compensation will actually come in the form of a prepaid Mastercard valued up to $700.
Eligible new hardware ranges from the iPhone 7 through to the iPhone X, excluding the iPhone 6s and SE.
T-Mobile regularly runs similar "BOGO" promotions, particularly in the months surrounding an iPhone launch.