Both 2G and 3G CDMA work in North America (which includes Mexico) and parts of Asia, South America and the former Soviet Union. Most of the non-North America CDMA world uses 3G CDMA. If you travel with CDMA make sure your handset is a 3G model.
There are a few odd areas in Europe that have limited CDMA service such as Portugal and Ireland, though they are on the 450MHz band that is not available on North American handsets. They are really GSM dominant countries.
Bottom line is that over 200 countries use GSM versus 81 countries, mostly in Asia that use CDMA of various types. Not all are compatible. One example is Nextel IDEN that runs over CDMA is not compatible with any other CDMA network. Another example is PCS. There are also frequency differences. AFAIK there is no CDMA handset that can communicate on all the CDMA frequencies unlike international GSM handsets that can.
Handset rental is very expensive at ~$8 per day plus a one time $15 delivery charge. Set up charges and usage charges are on top of that. Typical minutes rates are $2.
By contrast roaming in the EU with my AT&T GSM handset costs $2 per minute. If I purchase a prepaid SIM for the handset, there are no roaming charges because I have a local number. The SIM costs about $15 and the usage charge is ~$0.10 per minute. Once the SIM is purchased it is yours for future use. It can be easily recharged with additional minutes as necessary. I keep SIM cards for each country I visit on a regular basis.
