GameStop wants to buy your iPhone 5S, even though it doesn't officially exist yet (Updated)

GameStop sure is on top of its game these days. Not only does the company -- which has made a name for itself as a reseller of used video games -- accept trade-ins on a litany of devices ranging from BlackBerry smartphones to Android tablets, but it will even offer a hefty sum for your nonexistent iPhone 5S. As you can see by the screenshot above, GameStop has added the not-yet-official, next-gen Apple smartphone to its list of accepted devices, complete with its own trade-in values.

So how much is an unreleased phone worth these days (or, more accurately, how much will the iPhone 5S be worth once it's actually available to purchase)? Let's compare the iPhone 5S trade-in values with that of the iPhone 5:

iPhone 5 ("Like New" condition):
16GB (AT&T) - $390 (store credit), $310 (cash)
32GB (AT&T) - $458, $364
64GB (AT&T) - $466, $370

iPhone 5S ("Like New" condition):
16GB (AT&T) - $480 (store credit), $382 (cash)
32GB (AT&T) - $530, $422
64GB (AT&T) - $580, $462

As of this writing, the GameStop trade-in website only has AT&T models listed for the iPhone 5S, whereas the iPhone 5 has carrier options that include T-Mobile, Verizon and Sprint.

Update: GameStop has now pulled the iPhone 5S listings from its trade-in page.