Selling 3gs and 3g iPhone to buy iPhone 4

[curtishd]

So I will be selling my 3gs and wives 3g to pay for the new iPhone 4. What do I need to do to sell these? Remove sim cards? Restore? Anything else to have all my data gone so no one can access my info or web info?
Also where is the best place to sell them and what is a good price to sell at?

 

[citron230]

seriously, tons of threads. searching will get you your answers fast