New Iphone for Christmas present.

Im really wanting to get my boyfriend the new iphone for christmas since he already has a plan with at&t. The only problem is I don't want him to know until christmas and then after christmas we both go in together to get his phone number transferred over to the iphone. My question is, is there anyway to just buy the iphone with out switching the contract over to the new phone or getting a new one? Because right now all I want to do is basically get an empty sell of a phone. lol