DTMF is the official name for the short beeps you hear when you press buttons in a phone menu. In VoIP, these beeps are not just sounds — they’re clear signals that tell your phone system what the caller wants to do.

What Is DTMF in VoIP?

DTMF is a form of tone dialing: every key sends a pair of tones, and VoIP platforms, PBXs and IVR systems “listen” to those pairs and turn them into digits or commands.

How DTMF Works Behind the Scenes

When a caller presses a key, the phone sends two tones at once. The VoIP system recognizes this combination, converts it into a digit, and your IVR or routing rules decide what should happen next.

Why DTMF Sometimes Fails in VoIP

DTMF often breaks when compressed codecs distort tones, device and provider use different DTMF modes, or gateways/PBXs change the media stream. Switching to RFC2833/RTP events, using G.711 and aligning DTMF settings on phones, PBX and provider usually solves the problem.

How Businesses Use DTMF VoIP

DTMF runs IVR menus, call routing, PIN or account entry, agent keypad shortcuts, and voicemail or conference controls — basically, any place where a caller “talks” to the system with their keypad.

Example: DTMF in a Real VoIP Setup

A customer calls a Freezvon number, hears “Press 1 to check your order,” presses 1, and the DTMF signal goes to the PBX. After the caller keys in the order number, the system finds it in the database and plays the status back.

FAQ: DTMF (Dual-Tone Multi-Frequency)

What is DTMF?

It’s a way to send keypad digits using pairs of audio tones.

Why can’t the IVR hear my tones?

Usually because of the wrong DTMF mode, codec issues or network equipment blocking or changing the tones.

What is DTMF relay?

It’s sending “digit pressed” information as RTP or SIP events instead of just raw audio tones.

How is DTMF used in a call center?

For IVR navigation, entering account data, agent commands and conference controls.

How do I enable DTMF?

Use the DTMF mode your provider (or Freezvon) recommends, set it on phones and PBX, then test it on an IVR or voicemail menu.

In Simple Terms

DTMF is the “beep language” of the phone keypad. In VoIP it turns into clean digital signals, so menus and call centers can clearly understand every key a caller presses.