Yet another retailer really wants your old phone and is willing to give you something pretty decent in exchange for it. Through Sept. 16, Best Buy is offering a minimum $100 trade-in credit to customers who trade in their old phones and switch to an iPhone 5.

Of course, it’s not as simple as just going in, handing in your old phone, getting an iPhone 5 and saying thank you very much. Just like the trade-in deal announced by Walmart, you’ve got to sign up for a two-year contract with either AT&T, Sprint, or Verizon Wireless.

Those looking to simply sell their old smartphones and pay full sticker price for a new device in order to avoid a new contract have several options, from listing your phone on eBay or Craigslist to Apple’s own trade-in program to services like Gazelle that buy used electronics.

Why is everyone so hot on trade-in programs at the moment? The main reason, as we’ve explained before, is the huge market in developing countries for used smartphones. Consumers in these countries often have to pay full price for their devices, so many of them are willing to pay slightly less for previously owned phones.

Second, as GigaOm’s Alex Colon points out, Best Buy is probably flush with inventory on the iPhone 5, which is being replaced by the iPhone 5C. This trade-in program helps clear that inventory, making room for the new devices, while earning Best Buy a commission on all the new wireless contracts it brings in during the promotion.

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