I know GSM is way better, however, CDMA is cheap and is someking of "open source" technology, that is growing very fast here in Mexico.
For those who don't know AMPS are analog phones, and TDMA 900/1800 is widely used in Canada, USA and Mexico, as well as CDMA.
GSM is mostly on Europe and Asia.
3G is finding it's still finding its way in Japan.
I read a few months ago about a british product that is just as cool as 3G phones but it works on lower-cost infrastructure, i think it even uses GSM.