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).

And that $300 discount? How it’s doled out depends on the trade-in value of your phone. T-Mobile says that any iPhone from the iPhone 6 or newer — except for the SE— qualifies, but you’ll only get credited upfront for whatever the carrier decides your current iPhone is worth.

If you upgrade early, you might forfeit some of your discount

Anything beyond that trade-in value toward the $300 total discount comes in the form of 24 monthly bill credits. So, hypothetically, if your iPhone has a trade in value of $200, you’ll get that up front, with the extra $100 split up among 24 monthly discount.

And like most of the other carriers, while you’re eligible for an upgrade after the first 12 months of payments, doing so means that you’re forfeiting what remains of your monthly discount — so it might be worth trying to flip your old iPhone by other means and just buying an iPhone X outright with the profits if you’re planning on upgrading more frequently.

And if you need a refresher on T-Mobile’s iPhone X prices, your various options are below:

Through the Equipment Installment Plan (i.e., a spacing out the cost of the phone across 24 months:)

64GB: $279.99 down, with $30 per month payments for 24 months (for a total retail value of $999.99)

256GB: $429.99 down, with $30 per month payments for 24 months (for a total retail value of $1,149.99)

Jump! On Demand (T-Mobile’s rental program)