Telephone, device for communicating sound, particularly speech, commonly by resources of wires in an electric circuit. The telephones now in common use elaborated from the device fictional by Alexander Graham Bell and patented by him in 1876 and 1877. An apparatus including a transmitter used for transforming the acoustic signals of a human's voice to electrical signals, a receiver for changing electrical signals to acoustic signals and related signaling devices for communicating with other humans using same apparatus connected to a network. The term telephone also assigns to the elaborated system of transmission paths and switching points connected to this instrument. See also Telephone service.

The transmitter is a transducer that transform acoustic energy into electric energy. The carbon transmitter was the key to practical telephony because it amplified the power of the voice signal, making it possible to communicate over distances of many miles. Many of these transmitters are quiet in service, but they are gradually being replaced by designs based on the charged electret or on electrodynamic principles. Both the electret and electrodynamic transmitters use transistors to offer needed power gain; they originate less falsification than the carbon transmitter. See also Electret transducer; Microphone; Transducer; Transistor.

The receiver transducer functions on the relatively low power used in the telephone circuit; it transform electric energy back into acoustic energy. Different a loudspeaker, the telephone receiver is intention for close coupling to the ear. As in the transmitter, cautious device of the relationship of the acoustical and electrical elements generates a passion response-frequency distinguishing.

Standard telephone sets generally two cords: a line cord that links the apparatus to the building wiring and telephone network, and a handset cord that joints the telephone handset to the chassis. Cordless telephones use a two-way radio link between the handset and the base unit, which is same to the chassis of the standard telephone; this changes the handset cord. The base unit is jointed through a normal line cord to the telephone network.

Cellular telephone or cellular radio, telecommunications system in which a mobile radio transmitter and receiver or telephone is connected via microwave radio frequencies to base transmitter and receiver stations that joint the user to a conventional telephone network. The geographic region act by a cellular system is subdivided into areas called cells. Each cell has a central base station and two sets of allocated transmission frequencies; one set is used by the base station and the other by mobile telephones. To allow radio interference, each cell uses frequencies different from those used by its surrounding cells, but cells adequate reserved from each other can use the same frequencies. When a mobile telephone leaves one cell and enters another, the telephone call is transferred from one base station and set of transmission frequencies to the next using a computerized switching system.