GSM vs CDMA
GSM stands for Global System for Mobile Communication.
GSM is the dominant 2G (second generation) digital Wireless Cellular Phone standard for most of the world. It determines the way in which Wireless Cell Phones communicate with the land-based network of towers.
GSM is one of two major Wireless Cellular Phone technologies in the U.S. The other is CDMA. AT&T Cingular and T-Mobile use GSM. Sprint and Verizon use CDMA. GSM is more prevalent in most other parts of the world, and especially in Europe. Although they use the same techonology the USA uses the frequencies 900 and 1800 and Europe uses 1900. Only triple or quad band Wireless Cell Phones using GSM can be used internationally in both the US and in Europe.
World Roaming
Some Wirelless Cell Phones are designed to work in multiple parts of the world. Since GSM is the only digital technology used worldwide, that is the technology used by all "world Wireless Cell Phones".
Since different frequency bands are used in different parts of the world, world Wireless Cell
Phones support several of these bands. The USA uses 900 MHZ and 1800 MHz (PCS) for GSM, and
Europe uses 1900 MHz.
World Wireless Cell Phones support 1900 MHz and at least one of the European frequency bands.
Most of Africa and parts of Asia use the same bands as Europe. This enables world Wireless Cell
Phones to operate in most parts of the world.
Although GSM and CDMA Wireless Cell Phones provide similar basic features and services to
end-users, (such as voice calling, text messaging, and data services,) they operate very
differently at many technical levels. This makes GSM Wireless Cell Phones completely
incompatible with CDMA networks, and vice-versa.
The most visible feature of GSM are SIM cards. SIM cards are removable, thumbnail-sized smart
cards which identify the user on the network, and can also store information such as Cell Phone
Numbers. SIM cards allows users to switch Wireless Cell Phones by simply moving their SIM card
from one Wireless Cellular Phone to the other.
NAM
Number Assignment Module.
A part of the phone that stores a wireless device's phone number, lock code, timer reset code and
other user information. The NAM is programmed by the Wireless Plans service provider when a
device is activated.
The NAM also associates the Mobile Identification Number (MIN) with the Electronic Serial Number
(ESN).
Some Wireless Cell Phones have dual or multi-NAM features which allows two user to have more
than one Cell Phone Numbers. (Two "lines" on one phone.)
CDMA
Code-Division Multiple Access.
CDMA is a digital Wireless Cellular Phone technology. It is a general type of technology,
implemented in many specific technologies. But the term "CDMA" is also commonly used to refer to
one specific family of technologies (IS-95 and CDMA2000) that competes with technologies such as
GSM.