As early as the eighteenth century, the word "telephone" was used in Europe to refer to a microphone strung together with wires (a cup strung together with wires) The telephone was attributed to Alexander Graham Bell. 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. Bell applied for the telephone patent in March 1876.
The improvements and inventions of telephone in history include: toner microphone, manual switchboard, dial, automatic telephone exchange, program-controlled telephone exchange, dual-tone multi-frequency dialing, voice digital sampling and so on. In recent years, new technologies include ISDN, DSL, VoIP, analog mobile phone and digital mobile phone.