Do I have to sign a contract when I purchase the new 3g iPhone if i dont have service already?

I hate contracts and i know that i can purchase the phone from the Apple store on July 11th without signing a contract at all, but in order to get data service do i need to sign a contract? Please help!
i know that regularly if you walked into an AT&T store with your own AT&T phone and needed service, you dont need to sign a contract. The contract is usually used as an incentive to get you to purchase a new phone at a cheaper price. Is this the case with the iPhone too?
I know there are no discounts on the new 3g iphone, its already being subsidized by Apple. my main questions is do i have to sign a contract to have service? Other phones you dont have to, but is the iphone different?