I currently have a 3GS w/o a data plan on ATT, and I got some people on Craigslist who would buy my iPhone for $350 ( I live in California). I'm planning on getting the iPhone 4 32 Gb. once it comes out, but I was wondering if it would only cost $299 for the phone. Are there any other taxes or other fees that you need to pay? I really want my sold iPhone 3GS to cover all the costs of the iPhone 4... What you guys think?