DTMF (touch-tone)

What it is

Dual-tone multi-frequency signalling is the pair of tones each keypad digit produces. Every phone and every carrier supports it, and unlike speech it has no accent, no background noise and no ambiguity between "fifteen" and "fifty". Traditional IVRs are built on it. Voice agents can accept it alongside speech if the platform passes the tones through and the conversation design uses them.

Why it matters when buying

Three situations call for keypad input even in a natural-conversation agent. Long identifiers: a sixteen-digit card number or a policy number is faster and more accurate typed than spoken, especially on a narrow-band line or from a caller with a strong accent. Consent and opt-out: "press 1 to agree" or "press 9 to be removed" produces an unambiguous, timestamped record, and some regulators and do-not-call regimes expect an easy opt-out mechanism on automated calls. Fallback: when speech recognition has failed twice, offering the keypad keeps the call alive instead of transferring or hanging up.

Some SIP paths strip or garble tones unless configured for out-of-band DTMF, so this is also a telephony question.

What to ask

Ask whether the agent accepts keypad input mid-conversation and whether it can prompt for it when speech fails. Ask how keypad entry of sensitive numbers is masked in transcripts and recordings. Ask whether opt-out by key press is supported and logged. In the demo, enter a number on the keypad without being asked and see whether the agent uses it.