CDMA is an acronym for Code Division Multiple Access; it is a digital technology that uses what is known as ?spread spectrum techniques.? This means that the transmitted signal frequency varies deliberately. Allowing the signal to vary gives an output of more bandwidth than would be allowed if the frequency was not varied. CDMA has long been the standard used in the USA and has been known for its ability to provide better voice and data services than other cellular technologies on the market. Verizon and Sprint use CDMA technology.
What Is GSM
GSM is the acronym for Global System for Mobile communications; it is a digital technology that assigns a fixed frequency every user on their network. GSM is the current standard in most of Europe, Asia, and has made rapid strides in gaining market share in the USA. GSM mobile phones use SIM card technology. AT&T and T-Mobile use GSM technology.
SIM and R-UIM
A SIM card is a small removable smart card that allows users to easily switch between handsets while retaining their personal contact information and address books. The SIM card is tied to the carrier's network and can be moved without intervention from the carrier. Activating a new phone on a GSM network is as easy as putting an activate SIM card into it. GSM phones with a removed SIM card can later be used again as soon as a SIM card is placed into it.
CDMA phones are not card-enabled; this means that the cell phone used on the CDMA networks can only be used on those networks. The phone itself is tied to the carrier's network; you cannot switch to a new CDMA phone without first talking to your carrier and having them deactivate your old phone and then activating your new phone on their network. Once the old phone has been deactivated it then becomes useless.
The CDMA equivalent to a SIM card is called an R-UIM card; Removable User Identity Module. The R-UIM card is not yet available in the US market, currently only being available in parts of Europe and Asia.
Travel
You will find that both GSM and CDMA networks have good coverage in major metropolitan areas. When you find yourself roaming outside of your usual area you may find yourself without adequate coverage if you are on a CDMA network, especially if you enter into a more rural area. GSM carriers have contracts with other GSM carriers that will allow them to have better roaming coverage, even in rural areas. If you are going to travel internationally with a GSM carrier you will most likely have no problem getting a signal from an international carrier. Most carriers in international markets are GSM networks. You will need to check with your chosen carrier about the domestic and international roaming plans they can offer you.
TDMA
TDMA, or Time Division Multiple Access, is mostly in use in the Americas (North and South) and some parts of Asia. TDMA is not popular in widespread usage because of its lack of flexibility as it compares to the other two digital cellular technologies. Current cellular providers that are still using TDMA technology are predicted to switch over to the more popular and more flexible GSM technology.
