I don't know about the first part, but your friend will be locked in to a 2 year contract unless she jailbreaks it and goes with another carrier. The current offer is $199 for a new 3GS 16GB with a 2 year contract so your friend isn't getting any advantage by buying it from you rather than Apple (barring the jailbreak scenario).

You'd probably be better off selling it on craigslist or something similar--they command higher prices than retail since there are resellers who buy them for decent money, jailbreak them and then ship them overseas where they can get even more.