DTMF

• "Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the voice-frequency band to the call switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone, and is standardised by ITU-T Recommendation Q.23. Other multi-frequency systems are used for signaling internal to the telephone network."

See Also

• What are the ABCD DTMF tones?
• SIP DTMF
• DTMF Tester software by DIDX
• DTMF double Digit Problem on DID Number
• Asterisk DTMF
• CLID DTMF Sweden (relevant?)
• DTMF signals and IVR processing