Talk-Off, or Talkoff, is the term that describes when a human voice is able to trigger touch tones, or DTMF tones during a telephone call. Talk-Off occurs when a signal processing system tries to translate sounds into to touch tones. Some people's voices are able to recreate touch tones frequently relative to the general population.
Human Voice as DTMF
Talk-Off is possible as human voices speak in the same frequencies as DTMF combinations. Unlike real touch tones generated using telephone keypads, human-voice created touch tones are not sustainable and can generally be isolated by algorithms created to determine true DTMF. However, occasionally a speech signal will momentarily contain strong frequencies in just the right frequency bands which then occur as DTMF sounds.