Telephone is a kind of remote communication equipment that can send and receive sound. The principle of early telephone is that sound is a compound vibration in the air, which can be transmitted to solids and to conductive metals through electric pulses.

In the history, the telephone has been improved and invented by color-coded microphone, manual switchboard, dial, automatic telephone exchange, program-controlled telephone exchange, dual-tone multi-frequency dialing, voice digital sampling and so on. This industry is usually divided into telephone equipment manufacturers and telephone network operators. Historically, network operators usually have a national monopoly position.

In recent years, with the opening and integration of the global telecommunications market and the development of technology, there has gradually emerged a situation in which many operators compete in the same market.