I just looked at a GSM global coverage map, it seems that most of the planet with the exception of North America and a few Latin American countries is GSM. What's the upside to CDMA? It seems like CD versus vinyl LP.
CDMA is only used in the US. The rest of the world is GSM. That is why CDMA phones have GSM radios -- so when you go overseas you can connect to their network.
What is the advantage? Nothing really -- it is just older technology. Verizon is working to phase it out (they will want all LTE in the future). Sprint is also trying to do this it will just be a lot longer road for them compared to Verizon.