The way we buy smartphones is changing rapidly, and now carriers are locked in a back and forth game of undercutting to provide users with the most attractive deals.

Earlier today, Sprint mildly adjusted its iPhone upgrade plan such that qualified customers can now trade in their existing smartphones and get a new iPhone 6s for just $15 per month. Without a trade-in, users can still get a new iPhone 6s for just $22 per month and an iPhone 6s Plus for $26.

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These deals are part of Sprint’s iPhone Forever program which was originally announced a few weeks ago. The buy-in prices Sprint is advertising today, however, are a bit cheaper than before and are undoubtedly a response to Apple’s own iPhone upgrade plan and T-Mobile’s $20/month iPhone 6s upgrade plan which it unveiled yesterday.

As long as the value of the phone you’re trading in is at least $90, Sprint’s deal is the best around for the iPhone 6s.

Apple, in case you missed it amidst a sea of product announcements this week, unveiled its own iPhone upgrade program where users can get a new iPhone every year with AppleCare+ for $32.41 – $44.91 per month depending on the model.

Updated to clarify that the value of your trade-in must be at least $90, otherwise T-Mobile has the better deal.