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Documentation Index

Fetch the complete documentation index at: https://www.bolna.ai/docs/llms.txt

Use this file to discover all available pages before exploring further.

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What is DTMF?

DTMF (Dual-Tone Multi-Frequency) is the system behind phone keypad input: the tones produced when a caller presses a digit key (0-9, *, #). When enabled, digit presses from the caller are captured and sent to the agent as a text message, which the LLM can read and respond to just like spoken input.

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When to use it

DTMF is useful any time you want callers to enter structured numeric input without speaking it:
  • PIN or OTP verification — “Please enter your 6-digit OTP followed by #”
  • Account or order number lookup — “Enter your account number and press #”
  • Phone number capture — collecting a callback number during a call
  • Confirmation flows — “Press 1 to confirm, 2 to cancel”
  • Sensitive input — when callers are uncomfortable speaking a number aloud (e.g. a password or card number)
DTMF works alongside speech. A caller can still speak normally between keypad entries.
For branching menu flows (“press 1 for sales, press 2 for support”), use IVR Inbound Calls instead. It handles menu routing natively without an LLM.

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Telephony support

ProviderSupport
PlivoSupported
TwilioSupported
SIP Trunk (BYOT)Currently not supported
ExotelCurrently not supported
VobizCurrently not supported

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Enabling DTMF

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From the dashboard

Toggle on Keypad Input (DTMF) in the Call Tab of your agent.
Call tab showing the Keypad Input DTMF toggle

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Via the API

Set dtmf_enabled: true inside task_config when creating or updating an agent: 
{
  "task_config": {
    "dtmf_enabled": true
  }
}

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How it works

  1. The agent asks the caller to enter digits and press #.
  2. The caller presses keys on their keypad.
  3. Bolna accumulates the digits until # is pressed.
  4. The digits are delivered to the agent as: dtmf_number: <digits>
  5. The agent responds to the input.
# is the termination key. The agent only receives the input after the caller presses it. The # itself is not included in the value.

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Writing the prompt

Tell callers to press # after their entry, and tell the agent what to do when it sees a dtmf_number: message. Example prompt snippet: 
When you need the caller's phone number, say:
"Please enter your phone number on your keypad and press the hash key when you are done."

When you receive a message starting with "dtmf_number:", the digits that follow are what the caller entered.
Read them back to confirm and proceed accordingly.
What the agent receives: 
dtmf_number: 9876543210
The agent treats this like any other message in the conversation. It can confirm the value, use it in a tool call, or move to the next step based on it.

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Next Steps

IVR Inbound Calls

Menu-based call routing with keypad navigation

Call Tab

All call configuration options