Voicemail Detection Assistant for Outbound Calls

An outbound calling assistant that monitors transcriptions to distinguish between voicemail systems and live humans. When voicemail is detected, it triggers a tool to deliver a pre-recorded message. For live contacts, it delivers a brief message and handles responses professionally before ending the call.

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The numbers

latency—

cost / min—

frameworkVapi

The stack

telephonyTwilio SIP

speech-to-textDeepgram Nova-3

llmClaude Sonnet 4.5

text-to-speechCartesia Sonic-3

System prompt

No prompt published.

Config

config.json

{
  "tools": [
    {
      "name": "leave_voicemail",
      "description": "Leaves a pre-recorded voicemail message when voicemail is detected",
      "type": "voicemail",
      "beepDetectionEnabled": false
    }
  ],
  "firstMessageMode": "assistant-waits-for-user",
  "voicemailMessage": "",
  "voicemailDetectionEnabled": false
}

Tools

leave_voicemailLeaves a pre-recorded voicemail message when voicemail is detected

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