aye CDMA will only run on CDMA carriers and same with the GSM version - it just depends on what carrier you want to run it on. sprint/verizon/alltel/qwest are all CDMA and at&t/t-mobile are the two big GSM carriers for the US. In Europe GSM is pretty much the standard and most (all in many countries) are GSM. careful getting an overseas GSM version as these
afaik will not do 3g data in the US even on at&t/t-mobile (at least at the moment).