This is intriguing: 9to5Mac is claiming that they've heard from multiple sources that GameStop will be carrying iOS devices, including iPhones, iPads, and iPod touches, in the very near future. The announcement was supposedly made last week to the various store managers at their annual gathering in Las Vegas, and the biggest indication that this is so is that GameStop has actually mentioned accepting trade-ins for the devices on its website. That system doesn't appear to be fully up and running yet, but yeah: You'll be able to trade in your iOS device to GameStop in the future.
That's pretty wild -- we'll have to wait and see how it all works, including which service provider GameStop uses for selling iPhones, and all of the other issues that might pop up around a system like this. It's unclear what value the store will assign to these devices as well; GameStop traditionally allows customers to trade-in items either for store credit or a lesser amount of cash, and that value is obviously less than they sell the devices for afterwards.
We'll just presume that all of those questions will be answered in time (probably, guesses 9to5Mac, in accordance with the upcoming rumored iPhone 5 release). GameStop has recently been trying to deal with the flood of digital game sales in marketplaces like the App Store, but this looks like the company is going with a new strategy of "joinin' em," rather than beating them.