Communications devices are used to send and receive messages over a distance. A PHONE is a device that uses electrical signals to transmit sound, usually between two people. An intercom is a device that allows two-way communication within a building or other enclosed area. A RADIO is an electronic device that transmits and receives electromagnetic waves, allowing for wireless communication. A telex is a device that sends and receives typed messages over telephone lines. A walkie-talkie is a portable two-way RADIO transceiver. Finally, a rotary telephone is an analog telephone with a rotary dial, which was the most common type of telephone until the 1980s.