I went from AT&T to Sprint because AT&T's service is terrible in my area. When I picked up my 4S yesterday at a Sprint store, they purchased my used 16 GM black iPhone 4 for $250. I would say it was in good condition with a few scratches on the screen and normal wear and tear throughout the rest of the phone. When I checked eBay Instant Sale, a "good" condition 16 GB iPhone 4 was going for $200 so I felt like the $250 was a steal. I'm sure I might have been able to get a few bucks more through Craigslist or just putting my own auction up at eBay but I'm not sure it would have been worth the hassle.