Best Buy will trade you a free iPhone 5 for your old smartphone

Don’t know what to do with your old Palm Pre? If you were thinking about getting an iPhone(s aapl) you can bring it to Best Buy(s bby) this weekend, where it’ll take your old smartphone and give you an iPhone 5 in exchange. From now through September 16, Best Buy is offering customers a guaranteed minimum $100 trade-in credit for any working smartphone as long as you switch to the iPhone 5 on AT&T(s t), Sprint(s s) or Verizon(s vz) with a two-year activation. Provided you don’t want the iPhone 5c or 5s instead, that isn’t a bad deal.

When Apple introduced the iPhone 5s and the iPhone 5c on Tuesday, it announced that the iPhone 5c would replace the iPhone 5. Both phones are virtually identical, aside from the colorful new plastic build quality of the iPhone 5c and its slightly extended battery life. The iPhone 5c will also start at $99 on a two-year contract. So if you’re looking for iPhone 5c power in a more staid design, the iPhone 5 is the phone to get.

But you need to hurry. Not just because Best Buy’s promotion ends on Monday, but because the iPhone 5c has already gone on pre-sale. Come next week it’ll be on store shelves and the iPhone 5 will be history.

This promotion makes sense for Best Buy, allowing it to clear as many remaining iPhone 5 handsets out of inventory as it can before the phone disappears into the digital ether. But it also makes sense for customers holding on to very old smartphones. That Palm Pre, for instance, isn’t going to get you much money anywhere else. (I just checked, and Amazon(s amzn) is graciously offering up to a $0.75 gift card for it.) And if your old phone is worth more than $100, Best Buy will give you the difference in the form of a gift card.

Best Buy didn’t rank high when I surveyed the best places to sell your old iPhone a couple of weeks ago, and you probably don’t want to try an old iPhone in there now, either. But if you’ve still got an original Motorola(s goog) Droid burning a hole in your pocket, this new deal is worth a look.