Can i buy the iphone 5s if I already have contract with AT&T?

I wanna buy the iphone 5s. But I already have contract with AT&T. So can I go straight to Apple retailer and buy it with full price $649.99. Or I have to make the new contract to buy iphone 5s?

You need to make a new contract. You're also going to need to go through an early termination fee of $350.