On October 13, 1983, Ameritech Mobile Communications (now AT&T) established the United States’ first cellular network in Chicago, Illinois. Reliable cellular networks make widespread use of mobile technology possible. A cell is a geographic region served by one cell tower. A cell tower, sometimes called a cell site or base station, is a radio transceiver. This means the tower can both transmit radio signals as well as receive them. A cellular network is simply a connected series of cells. Each cell operates on a distinct radio frequency. This allows mobile devices to access widespread coverage without a disruption in service as the user enters and exits each cell. Today, cellular networks are available all over the world. In the developing world, cell phones are more reliable and popular than traditional landlines. Millions of people rely on cellular networks for personal, business, and health-related communications.