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CDMA operates by converting data and voice into digital information, and transmits such signals over a wireless network. According to the CDMA Development Group (CDG), CDMA network supports over 270 million subscribers around the world. It is also the basis for the 3G technology that offers enhanced voice capacity and data transfer rates. Carriers that use CDMA in the nation include Verizon Wireless and Sprint.

GSM, on the other hand, is the dominant 2G standard and the most popular network technology worldwide. It digitizes data and sends it down a channel with two other streams of user data, while each of them has its own time slot. The technology currently serves over 3 billion people across 219 countries and regions, according to GSM Association. Both AT&T and T-mobile offer nationwide GSM network.

Apart from the background facts mentioned, CDMA and GSM actually operate very differently in many technical aspects.

Subscriber Identity Module (SIM) cards
Carriers using CDMA in the U.S. require proprietary handsets. The cell phones are linked to one carrier only and are incompatible with any SIM card. To upgrade a CDMA phone, users must have the carrier deactivate the old phone and activate the new one.

However, GSM phones can work with SIM cards, which are tied to the respective carrier but not the actual handset. Users can swap between card-enabled phones anytime, without considering the carrier.

Data Transfer Methods and speeds
Concerning data transfer, CDMA offers a high-speed technology 1xRTT (Single Carrier Radio Transmission Technology), which is able to provide ISDN (Integrated Services Digital Network)-like speeds of up to 144Kbps. It also has another data transfer method for the 3G system called CDMA2000, which offers downstream speeds closer to 300-700Kbps.

Meanwhile, GSM provides a high-speed data technology called GPRS (General Packet Radio Service), but it offers a slower data bandwidth for connection. EDGE (Enhanced Data Rates for GSM Evolution) is reported to have speeds closer to 70-140Kbps. With continued improvement, speed of data transfer with EDGE has been reportedly increased to about 275-380Kbps.

Actually the 1xRTT technology is more advanced than EDGE, since it gives higher transfer rates. However, it requires a dedicated connection to the network for use, while GPRS sends in packets and will not block out voice calls when making data calls.

International Roaming
CDMA network is not equipped with multi-band capability, so it cannot be used abroad. However, GSM phones can be used in many parts around the world, as long as they are qual-band or tri-band devices (850/900/1800/1900 MHz). The user can also buy a local SIM card in the country he/she is visiting and make calls with the card, so as to save international roaming charges.

As GSM networks continue to expand services in the U.S., while CDMA networks also make progress in other parts of the globe, it is expected that the competition between the two network technologies will definitely become even keener in the future.

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