I'm looking into selling my 3gs 32gb that is in perfect condition to fund the new iphone 4... but first I have some quesstions.

About how much should I be able to get for my phone?

Would I be able to sell my phone now... put my sim card in an old phone for a couple weeks, and then just bring in my Sim card only to activate my new iphone 4 that I purchase at the Apple store?

Can you resign a new 2yr agreement with ATT even if I resigned 7 months ago? Will this resigning allow me to get the iphone 4 32g at the 299 price?

Thanks for the help guys!