VERIZON = CDMA :
SIM cards are used with carriers that operate on the Global System for Mobile Communication Or G.S.M .
that operate on a system called T.D.M.A
The competing network is Code Division Multiple Access CDMA a technology created in the U.S. By the company Qualcomm.
As of fall 2005, CDMA cell phones and CDMA carriers do not support SIM cards in most parts of the world .
this might be changing. A CDMA SIM card called the R-UIM (Re-Useable Identification Module) was made available in China in
2002, and might eventually be available worldwide.
Code division multiple access
CDMA is a special coding scheme where each transmitter is assigned a code to allow multiple users to be multiplexed over the
same physical channel
CDMA was first used by the military and uses spread-spectrum technology, decreasing potential interference while achieving privacy.
Time division multiple access is a channel access method for shared medium networks.
It allows several users to share the same frequency channel by dividing the signal into different time slots.
The users transmit in rapid succession, one after the other, each using his own time slot.
This allows multiple stations to share the same transmission medium (e.g. radio frequency channel)