Short for Dual Tone Multi-Frequency, the system used by touch-tone telephones. DTMF assigns a specific frequency (consisting of two separate tones) to each key so that it can easily be identified by a microprocessor.
DTMF FAQ This FAQ contains an introduction to DTMF, information on how to decode DTMF, a list of DTMF-receiver chips, links to manufacturers, and a section on DTMF in C.
Generating DTMF tones Provides information on generating DTMF tones using a sound card.