Got my new iPhone 5s last Tuesday, dropped my 4S 16GB in the mailbox on Saturday, Gazelle got it on Monday, and I just got confirmation a few minutes ago that I'm getting $236.25 for it in a few days, which covers the price of the phone and AT&T's upgrade fee. I locked in the price at its peak.
Prices have not dropped that much since the new phones came out, even though they're giving away 4Ss for free. See
how much different iPhone models are going for. It looks like more memory doesn't help the resale value much, but carrier makes a big difference, with AT&T leading the way. Always say it's flawless, if it's not badly messed up, the worse that'll happen is they knock ten bucks off if they disagree. And did you know that Gazelle doesn't want the cords or accessories, so you get to keep all those, that's worth like $70 bucks if you buy them separately new from Apple, and it's always convenient to have spares. (So, the 30-pin plug doesn't fit the new phone, but it still fits my iPad 2.)