What (who) is DTMF - definition

Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized as ITU-T Recommendation Q.23. It is also known in the UK as MF4.

Touch-Tone dialing with a telephone keypad gradually replaced the use of rotary dials and has become the industry standard in telephony. Other multi-frequency systems are also used for signaling on trunks in the telephone network.