I just thought I would add my 3c worth in as a 3G engineer.
As someone who has worked on both technologies for many years, CDMA is probably the better engineered network - I think this was due to Qualcomm owning most of the patents on the technology - you can fine tune the whole system a little better than what you can with UMTS. Plus, the range at any given power is slightly greater for CDMA. It was a very cleverly designed system that was unfortunate in that Qualcomm doomed it.
Where CDMA was let down was Qualcomm overcharging for it, litigating against Nokia who was keen to develop handsets for it over patents.
So these days UMTS is the system that everyone is using, the upgrade from GSM is pretty clearly defined - many operators have a core network that is designed operate with both GSM and UMTS access networks.
I think GSM service providers are much more focused on the quality aspects...
Once upon a time, I had a reliance CDMA mobile, but I didn't enjoy using those services as compared to my IDEA, HUTCH and other GSM service providers...
So, I vote for GSM...
Parag V. Soni-reply by Parag
I have tried a GSM service in the US. CDMA is a better service. I have service in many places, like mountains, valleys, and in the middle of the desert. My main reason for having a phone is to make phone calls. In this regard, GSM sucks in the US. There were too many times I had to walk up and down a sidewalk or stop and start my car to get a signal with GSM. When I finally switched to CDMA it was a breath of fresh air. I don't ever worry about a signal now. If I cant talk, nobody can and generally I am the only one with service when in a group of people with GSM.
It may be good in Europe, but in the US it is the runnerup.-reply by Dwight Palmer
Basically the communication in the wireless world between 2 people can be accomplished by dividing the medium into time or frequency or codes.If you assign time slots to a user then it is TDMA.If you assign codes to user then its CDMA.If you assign frequency slots to users then its FDMAAs far as security is concerned CDMA is best as when a code is assigned to a transmitted signal only the receiver whose frequency response is programmed with the same code can actually be able to intercept the signal.But the fact that CDMA phones don't work in multiple countries is a major negative point..The market share and popularity does go in favour of GSM.Even the way SIM works for GSM and the way it works for CDMA varies.The fact that a GSM SIM can be easily swaped from an old cellphone to a newer one with your data intact but incase of CDMA phones since all contact information gets stored in the operator's database so it works fine if the operator service is the same one.Well that again has a positive point with CDMA phones as incase the phone gets stolen there is always a way to recover the lost contact information.