DTMF stands for Dual Tone Multi Frequency, which is the oldest and the most widely used data format on two way radios. This format was invented by Bell Telephone for telephones. DTMF is actually the generic term for Touch-Tone which is a registered trademark of AT&T. A telephone has a DTMF generator that produces the tones as you dial the numbers.
DTMF is used in 2-way radio for station identification and for other control functions. In a two way radio, DTMF can be used to send an individual ID code every time a user pushes the PTT. This code informs receiving radios which user is calling them. In a low range, weak signal or noisy environments, it is sometimes difficult to recognize a radio caller. In such situations, these DTMF signals can be used to distinctly identify the calling radio.
This function has various uses such as selective calling individual radios, radio disabling, and for short messages to be transmitted and received in situations of emergency.