Acronym for Dual-Tone Multi-Frequency. DTMF is the signaling standard for
telephone handset push-button key pads. The keypad is a 4x4
matrix of frequencies; each button corresponding to two frequencies indicating a
row and a
column:
123A
456B
789C
*0#D
row tones 697, 770, 852, 941
col tones 1209, 1336, 1477, 1633