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This guide explains how to connect a Callr phone number to a Vapi voice AI agent using SIP.

• Callr handles telephony worldwide: phone numbers, carrier connectivity, call routing, SIP, reliability, compliance.
• Vapi handles real-time AI: speech recognition, reasoning, tool use, and speech synthesis.

➡️

The result: anyone can call your Callr number, and the call is handled live by your Vapi AI agent.

🏗️ Architecture Overview

1. A user dials your Callr phone number.
2. Callr receives the Inbound Call.
3. A Callr scenario uses dial@v1 to connect the call to a Vapi SIP endpoint.
4. Vapi answers the SIP call and runs your voice AI agent.
5. Audio flows bidirectionally between the caller and the AI.

⚙️Prerequisites

Before starting, make sure you have:

• A Callr account
• A purchased Callr phone number
• A Callr Actions scenario
• A Vapi account
• A created Vapi assistant

When SIP is enabled on your Vapi assistant, Vapi provides a SIP URI in this format:

sip:<assistant-id>@sip.vapi.ai;transport=tls

🤖 Step 1 – Configure Your Vapi Assistant

In Vapi:

1. Create or configure an assistant.
2. Configure:

• Model (LLM)
• Voice
• System prompt
• Tools (if needed)

3. Enable SIP connectivity for the assistant.
4. Copy your SIP URI:

sip:<assistant-id>@sip.vapi.ai;transport=tls

Vapi handles:

• Speech-to-text
• LLM reasoning
• Tool execution
• Text-to-speech
• Conversation state

Callr does not process AI logic - it securely transports the audio stream over SIP.

⚡ Step 2 – Create a Callr Scenario

Create a Callr Actions scenario that dials the Vapi SIP endpoint when your number receives a call.

description: Route inbound call to Vapi AI

compat:
  version: "2025-09-01"

defaults:
  autoAnswer: false

branches:
  inbound-call:
    actions:
      - action: dial@v1
        params:
          targets:
            - number: sip:<assistant-id>@sip.vapi.ai;transport=tls
              timeout: 60

How it works

• inbound-call is triggered when someone calls your Callr number.
• dial@v1 creates an outbound SIP call.
• The target is the Vapi SIP endpoint.
• transport=tls ensures encrypted SIP signaling.

🔗 Step 3 – Attach the Scenario to Your Phone Number

In the Callr dashboard:

1. Go to your phone numbers.
2. Select the number.
3. Attach the scenario you created.

Your number is now connected to the Vapi AI agent.

🧩 Optional – Add Fallback or Business Logic

Because routing happens inside Callr, you can add:

• Time-based routing (business hours vs after hours)
• Failover to a human agent if SIP fails
• Geographic routing
• Call recording (if compliant in your jurisdiction)
• Pre-call IVR before sending to AI

Example with fallback and call recording:

branches:
  inbound-call:
    actions:
      - action: startRecording@v1

      - action: dial@v1
        params:
          targets:
            - number: sip:<assistant-id>@sip.vapi.ai;transport=tls
              timeout: 20
            # this PSTN number will be called if Vapi fails to answer the call
            - number: '+33199001234' 
              timeout: 60
        result: $dial

      - if: '!$dial.ok'
        action: say@v2
        params:
          what: "Sorry, we are unable to connect you at the moment."

ℹ️

This keeps telephony logic inside Callr and AI logic inside Vapi.

🚀Why This Architecture Works Well

👍

Each platform focuses on its core expertise.