GSM or CDMA? (Score 2, Interesting)

I'm interested to see how this will work. Currently there are two big cellular standards: GSM and CDMA. GSM seems like the more viable choice, as it is used globally (three GSM nets in US, also), but many americans use CDMA carriers like sprint/verizon/alltel/etc. For either, I assume it would be just like hitting a roaming partner and associating with their network, but I wonder how they will prevent people from just using land-based carriers, assuming range permits this.