T-Mobile is rolling out a limited-time offer on the most expensive iPhone models, and this one doesn’t even require you to buy-one-get-one-free. Starting February 23rd, you’ll get $200 off the purchase of an iPhone X, iPhone 8, 8 Plus, 7 or 7 Plus via a prepaid Mastercard, which is nothing to turn your nose up at.

However, you’ll need to read the fine print quite carefully, because this offer requires a trade-in of a relatively recent flagship iPhone or Android device to qualify.

In order to get the $200 Mastercard, you have to trade in one of the following:

  • Samsung GS8 / Samsung GS8+ / Samsung GS8 Active / Samsung GS7 / Samsung GS7 Edge / Samsung GS7 Active
  • Apple iPhone 7 / Apple iPhone 7 Plus / Apple iPhone 6s / Apple iPhone 6s Plus
  • LG V30 / LG V30+

To be clear, you get the $200 on top of the value of your trade-in — this isn’t T-Mobile trying to buy a working iPhone from you for $200. But the trade-in requirement still means you’re going to have to evaluate this deal carefully, because carrier trade-in pricing tends to undervalue new phones particularly badly. For example, a 32GB iPhone 7 will get you an estimated $122 from T-Mobile, whereas they’re going on eBay for around $350. Things are even worse for old Android phones, which hold value less well than iPhones.

Still, if you have one of the older devices on the list (since the trade-in value for older devices is closer to the true resale value) and you can’t be bothered with dealing with Craigslist strangers, this is a good deal, especially on a premium device like the iPhone X, which doesn’t see many discounts.

Chris Mills has loved tinkering with technology ever since he worked out how to defeat the parental controls on his parents' internet. He's blogged his way through Apple events and SpaceX launches ever since, and still keeps a bizarre fondness for the Palm Pre.