VAPI inbound calling

VAPI provides powerful AI voice assistants, but these assistants need phone numbers to receive calls. SignalWire’s phone network can route incoming calls directly to your VAPI assistants using SIP trunking. This guide shows you how to connect them.

When you’re finished, callers will dial your SignalWire phone number and immediately connect to your VAPI AI assistant - no additional routing or servers needed.

Setup overview

What you’ll need

• A SignalWire account with at least one phone number (sign up here)
• A VAPI account with API access
• Your VAPI private API key (found in your VAPI dashboard)

Setting up VAPI to receive SignalWire calls

VAPI needs to know that calls will be coming from SignalWire’s network. We’ll create a SIP trunk that includes all of SignalWire’s IP addresses, then register your phone number with that trunk.

This follows VAPI’s official SIP trunk setup guide, but with SignalWire-specific configuration.

Create the SIP trunk

Run the API call below to create the trunk, making sure to replace YOUR_VAPI_PRIVATE_KEY with your actual API key.

Save the id from the response - you’ll need this credential ID for the next step.

$
curl -X POST "https://api.vapi.ai/credential" \
>
  -H "Content-Type: application/json" \
>
  -H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
>
  -d '{
>
    "provider": "byo-sip-trunk",
>
    "name": "SignalWire Inbound Trunk",
>
    "gateways": [
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      { "ip": "170.64.128.96", "inboundEnabled": true },
>
      { "ip": "198.13.56.186", "inboundEnabled": true },
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      { "ip": "104.248.176.184", "inboundEnabled": true },
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      { "ip": "152.42.144.114", "inboundEnabled": true },
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      { "ip": "104.248.150.114", "inboundEnabled": true },
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      { "ip": "138.68.125.160", "inboundEnabled": true },
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      { "ip": "159.65.244.171", "inboundEnabled": true },
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      { "ip": "167.99.198.84", "inboundEnabled": true },
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      { "ip": "13.245.35.235", "inboundEnabled": true },
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      { "ip": "108.61.169.31", "inboundEnabled": true },
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      { "ip": "137.184.4.155", "inboundEnabled": true },
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      { "ip": "188.166.126.7", "inboundEnabled": true },
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      { "ip": "139.59.34.94", "inboundEnabled": true },
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      { "ip": "165.232.186.228", "inboundEnabled": true },
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      { "ip": "157.175.131.128", "inboundEnabled": true }
>
    ]
>
  }'

Register your SignalWire phone number

Now register your SignalWire phone number with VAPI using the credential ID from above:

$
curl -X POST "https://api.vapi.ai/phone-number" \
>
  -H "Content-Type: application/json" \
>
  -H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
>
  -d '{
>
    "provider": "byo-phone-number",
>
    "name": "SignalWire Inbound Number",
>
    "number": "+15551234567",
>
    "numberE164CheckEnabled": true,
>
    "credentialId": "YOUR_CREDENTIAL_ID"
>
  }'

Make sure to replace:

• YOUR_VAPI_PRIVATE_KEY with your actual API key
• +15551234567 with your SignalWire phone number in E.164 format (including the + and country code)
• YOUR_CREDENTIAL_ID with the credential ID from the previous step

Assign your AI assistant

In your VAPI dashboard, find the phone number you just registered and assign it to one of your AI assistants. You’ll only need to configure the inbound settings - we’re not using this number for outbound calls.

Configuring SignalWire to route calls

Now we need to tell SignalWire where to send incoming calls. We’ll create a simple SWML script that forwards calls to your VAPI assistant.

Create the routing script

In your SignalWire dashboard, go to Resources → Add → Script → SWML Script. This script will handle all incoming calls by immediately connecting them to VAPI:

1
version: 1.0.0
2
sections:
3
  main:
4
    - connect:
5
        to: 'sip:%{call.to}@YOUR_CREDENTIAL_ID.sip.vapi.ai'

Replace YOUR_CREDENTIAL_ID with the credential ID from the VAPI trunk setup above. The %{call.to} variable ensures VAPI receives the original dialed number, which helps with call routing and analytics.

Connect the script to your phone number

Go to Phone Numbers in your SignalWire dashboard, find your number, and click Edit Settings. Under the voice settings, assign your new SWML script to handle incoming calls.

That’s it - your phone number is now connected to your VAPI assistant.

Testing and troubleshooting

Call your SignalWire phone number and you should hear your VAPI assistant answer within a few seconds.

If something isn’t working, here are the most common issues:

Calls aren’t reaching VAPI: Check that your SWML script has the correct credential ID and is assigned to your phone number. Also, verify that your phone number is set to accept voice calls.

VAPI can’t connect: Make sure all SignalWire IP addresses are in your VAPI trunk. If SignalWire has added new IP addresses since you created the trunk, you’ll need to update it.

Wrong number format errors: Phone numbers must be in E.164 format (+1234567890) with no spaces or special characters.

You can monitor call logs in both platforms - SignalWire shows the initial call routing, while VAPI shows the assistant interaction details.

What’s next

Now that you have basic inbound routing working, you might want to explore: