Honestly, if you need money, it's a decent idea. Especially if you scaled back to a different phone and got a cheaper plan.
I'm not broke or anything but every little helps so I'm just trying to get rid of things I'm not using before next summer rolls around. Plus I'm actually using the phone and only have four months left on my contract, so if I do decide to sell it it'll be one of the last things to go. Current priority is to get rid of games, DVDs etc. Can't drag a bookcase of 'em to university sadly and I just have way too much stuff taking up space in general.
I intend to sell my 360 on CL for like $20. I just want to get rid of it. No wires, no harddrive, just body with a controller. One of the first ones. lol. I'm mainly selling it for people who want to mod it or salvage bit and bobs.
I still have 25 PS3 games to sell, and now that we can't use our PayPal account...
Make a new PayPal account, then the money will be held until the buyer leaves feedback. No thank you. Nobody ever bothers leaving me feedback these days.