couple questions before I sell my iPhone 3GS

[bobright]

i am putting my iphone on ebay, i dont want to deal with the hassle of jailbreaking or unlocking so im listing as is factory restored with no sim card.

i am a current att customer but i want to wipe my phone clean before i ship it out as ill be getting the iphone 4. what do i need to do to wipe the phone clean, i restored now do i just take the sim out? should i set up as "new" phone in itunes or let the buyer do that?

any help would be appreciated, im curious if i take the sim out if theyll be able to make it function or if i need to set up as new phone in itunes for them...