Access Fee: Fee that local telephone companies are allowed to charge all telephone customers for the right to connect with the local phone network.

Airtime: Actual time spent talking on the cellular telephone. Airtime charges are normally more expensive during peak periods of the day and are generally less expensive during off-peak periods.

Cell: The basic geographic unit of a cellular system. A city or county is divided into small "cells", each of which is equipped with low-powered radio transmitter/receiver. The cells can vary in size depending on terrain and capacity demands. By controlling the transmission power and the radio frequencies assigned from one cell to another, the Mobile Telephone Switching Office (MTSO) monitors the movement and transfers the phone call to another cell and another frequency as needed.

ESN: Each cellular phone is assigned a unique ESN (Electronic Serial Number), which is automatically transmitted to the cellular tower station every time a cellular call is placed. The MTSO validates the ESN with each call. The ESN consists of three parts: the manufacturer code (cell phone), a reserved area, and a manufacturer- assigned serial number.

Frequency Reuse: The ability to use the same frequencies repeatedly across a cellular system. Since each cell is designed to use radio frequencies only within its boundaries, the same frequencies can be reused in other cells not far away with little potential for interference. The reuse of frequencies permits a cellular system to handle a huge number of calls with a limited number of channels.

Handoff: The process by which the MTSO passes a cellular phone conversation from one radio frequency in one cell to another radio frequency in another.

Hands-Free: An important safety feature that permits drivers to use their cellular phone without lifting or holding the handset to their ear.

Mobile Phone: The type of cellular phone that is installed in a motor vehicle. There are three main types of cellular phones mobile, transportable, and portable. A mobile unit is attached to the vehicle, draws its power from the vehicles battery and has an external antenna.

MTSO: Mobile Telephone Switching Office. The central switch that controls the entire operation of a cellular system. It is a sophisticated computer that monitors all cellular calls, tracks the location of all cellular-equipped vehicles traveling in the system, arranges handoffs, keeps track of billing information, etc.

NAM: The NAM (Number Assignment Module) is the electronic memory in the cellular phone that stores the telephone number. Phones with dual- or multi-NAM features offer users the option of registering the phone with a local number in more than one area.

Off-peak: The period of time after the business day has ended during which carriers may offer reduced airtime charges.

Peak: Highest-usage period of the business day when a cellular system carries the most calling traffic.

Portable: A one-piece, self-contained cellular phone. Portables normally have built-in antennas and a rechargeable battery.

Roaming: The ability to use your cellular phone outside your local calling area.

Standby time: The amount of time you can leave your fully charged cellular portable or transportable phone turned on before the phone will completely discharge the batteries.

Talk time: The length of time you can talk on your portable or transportable cellular phone without recharging the battery. The battery capacity of a cellular portable or transportable is usually expressed in terms of so many minutes of talk time OR so many hours of standby time. When you're talking, the phone draws additional power from the battery.

Transportable: The transportable cellular phone is a standard mobile phone that can be removed from the vehicle and used by itself with an attached battery pack. The entire unit is generally mounted or built into a custom carrying case.

Voice-activated Dialing: A feature available only on selected phones that permits you to dial numbers by calling them out to your cellular phone.