I think there is a very simple explanation for this. Apple hasn't figured out how to switch carriers via software! For example, if you get Verizon you just activate via the carrier. Then if you are traveling internationally you pop in a sim card. But then the phone wouldn't know if it should be looking for a GSM tower or a CDMA tower since its activated on two carriers now. Maybe a future software update will enable CDMA support for the 4S in the future, once Apple gets this right. Until then, I am sticking with my CDMA iPhone 4 (the main reason to upgrade for me would have been to go unlocked to use internationally, but that won't be coming for a while I guess). I doubt that the hardware is different and it contains a GSM only radio.