I could be wrong, but I remember reading that there is only 1 hardware model for the iPhone 4s. It supports both GSM and CDMA networks. The wikipedia article seems to support this claim: http://en.wikipedia.org/wiki/IPhone_4S#Hardware
That is correct - all 4s devices have both CDMA and GSM support; the difference between the AT&T and Verizon "versions" is just one of activation, basically.