I’ve recently had some cause to do some research into cell phone technologies. I need to buy a new cell phone and I’m a terrible shopper. I can’t buy anything without doing proper research. I also live near RTP where several big telecom makers are based. One of the many options i was presented when selecting a phone was the carrier technology, CDMA vs. GSM. Here is what I found to be the pros and cons of each.

Both technologies are digital which is different from the old analog cell format (FDMA) that still exists in the form of ‘roaming’ mostly in very rural areas. Most GSM phone won’t support analog at all, So if roaming in very rural areas is important then CDMA may be the only choice for you. Most CDMA phones will still support the old analog format.
CDMA – Code division multiple access.
This is a spread spectrum technology that makes very good use of the available bandwidth. It is used primarily by Verizon (possibly Sprint?) in my area and most of the United States. Korea and maybe India are the only other countries that use CDMA. Most other carriers in the US seem to use GSM.

GSM – Global System for Mobile Communications
This technology is based on TDMA or Time division multiplexing. This means the audio signal is ‘packetized’ and transmitted in small chunks

The issues:

Talk Time on phone:

CDMA has lower talk time than GSM because the transmitter (CDMA) is active all the time.
GSM has higher talk time than CDMA based phones because the transmitter (TDMA) does not require constant transmit. The transmitter can be idle when not actually transmitting packets

GSM clearly wins here? I have heard this point might be in error. CDMA might transmit at lower power because CDMA uses the frequencies more efficiently. I need to get better details on this.
Range to antennae: (US roaming)

CDMA allows greater range to antennae (110KM under ideal circumstances) and lower power transmitters (200mW) with greater range than GSM.

Lower distances to antennae (75-105KM under ideal conditions) than CDMA and Higher power transmitters (2W).

For urban areas this is probably a non issue but if rural travel and travel in areas where cell tower density is very low CDMA may win this point.

International Roaming:

GSM is clearly the winner here. Most or the world only supports GSM, albeit of 4 different frequencies. The phone you buy must support the frequency (1 of the 4) used in the country you wish to visit. GSM the more internationally accepted and has more international ‘roamability’ than CDMA

Patents and extra fees:

CDMA is patented by Qualcom – So additional fees need to be paid to Qualcom for its use. This limits its appeal in international markets.

GSM has no such patents and is an international standard.

Limited number of active calls per cell:

CDMA has no hard limit of number of calls per cell. the quality goes down the more calls are active and the provider may cap the total number of active users.
GSM has a hard limited number of calls per cell. Once the limit is exceeded you cannot use the cell.

Account and phone migration / upgrading.

GSM phones have a SIM card that carries all account/phone data. They can be ‘locked’ by the carrier but typically this can be circumvented by secret codes that are entered into the phone.
CDMA phones are typically specific to the carrier. (usually Verizon) and some migration services are offered by verizon for upgrades to other verizon phones.

Voice Quality:

GSM is commonly accepted to have better/clearer voice quality than CDMA

Total Market Size:

The market size for GSM is FAR larger in both number of subscribers and amount of total area covered.

This is true everywhere except the United States and Canada where it is the opposite. 71 million North American CDMA phones versus GSM’s 22 million as of 2003.
Fax/Web Data speeds:

Old Analog connections had very weak data speeds. (~19k)

Both technologies have poor standard data speeds. (~56k?)
Next generation techologies (3G) will supply much faster data throughput. Need info here on GPRS, EDGE, UMTS, 1xRTT, and EV-DO
Conclusion:

GSM seems to win overall for my money (for now). Although honestly the differences that matter are pretty small for me. I really don’t like being stuck with Verizon (Sprint?) as my only carrier. All things are in flux since new technologies are already in the works.
CDMA wins for best coverage in the US. The efficient use of spectrum gives CDMA a good technical edge over GSM. Given that I sometimes drive to rural areas that’s not a small issue.

GSM wins for talk time, voice quality, international roaming, upgradeability and probably price.
For my purposes I don’t really care about international roaming or the very best voice quality, but it really seems like the future is in GSM.

Data speeds being the biggest unknown issue here.

The added features of a phone such as GPS, WiFi may have more impact on why I would buy a specific phone.
Links:

http://www.mrvfone.com.au/vfone/techtop/gsm_cdma.htm

http://www.arcx.com/sites/CDMAvsTDMA.htm

http://pctoday.com/Editorial/article.asp?article=articles/2006/t0401/24t01/24t01.asp&guid=

http://www.wisegeek.com/what-is-the-difference-between-gsm-and-cdma.htm

http://www.hardwaresecrets.com/article/151

http://denbeste.nu/cd_log_entries/2002/10/GSM3G.shtml