Is it possible to buy the new iPhone 4 from Apple at full price and not sign up for a data plan?
No, that's not possible. All iPhones purchased from AT&T or Apple in the U.S. must be activated with a data plan. But subscribers can pay full price for the phone and not be tied to a contract. They can simply pay for their service month to month. And they are free to cancel the service at any time if they have paid full price for the phone.