I find it interesting that the OP said he didn't want any hassle and just wanted a buy back site, and then everyone suggested craigslist and ebay. Both those sites are full of hassles. I haven't sold on ebay in years, and every time I sell on craigslist I always get stood up at least twice when arranging to meet someone.
If you want the ultimate in hassle free, try GameStop. I haven't tried it myself, but I've heard good things and the prices they offer are competitive with Gazelle. The difference is you just take the phone into any GameStop store, the manager inspects it, and you walk out with cash. No need to wonder if your auction will meet the reserve price, no need to drive across town just to have some stranger not show up, no need to even find a box to ship it in. Yeah, there are ways to get more money, but this lets you just be done with everything and move on as fast as possible.