Cellular phones use a system of small areas, called cells, which have their own low power transmitter and receiver. Calls from phones in cells that are not adjacent to one another are carried over one of 666 frequencies. As one drives across the cells, a computerized switching system passes the call from one cell to another without disruption of the transmission. Cellular phones are advanced versions of the simple radiophones used by police and cab driver. The big difference, however, is that a radiophone uses only one transmitter which limits calls to about a 20-mile radius. Cellular phone systems with their vast network of cells allows calls to be made from any part of a city. More importantly, calls made on a cellular phone have the same high quality as calls made from a phone in one's home. Costs for the service will vary depending on the need, with differing rates for peak and off-peak hours. Some suppliers are offering flat rates for monthly service which may be preferable if you make a lot of calls. Consider what type of telephone you need. For security reasons you might want to consider buying a cellular phone with a detachable handset and antenna that can be stored in the trunk or glove box. Another feature is the electronic lock that prevents others from using the phone when you are not in the car. All cellular phones must meet minimum Federal Communications Commission requirements, but quality and features can differ widely. If possible, test the quality of the phone system in your area by asking local cellular companies if they permit road demonstrations. You may also be able to rent a car equipped with a cellular system. The equipment you purchase should be installed by a professional.