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Prerequisites

  • An active Twilio account
  • A Twilio phone number
  • Access to the Twilio console

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Step 1: Create a SIP Trunk in Twilio

  1. Log in to the Twilio Console
  2. Search for SIP Trunk in the search bar
  3. Click Create new SIP Trunk
  4. Give your trunk a name (e.g., “Rounded-Trunk”)

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Step 2: Configure Origination

Origination defines how Twilio handles outbound calls from Rounded.

  1. In your SIP Trunk, go to the Origination tab
  2. Click Add new Origination URI

  1. Configure:
    • SIP URI: sip:sip.callrounded.com;transport=tcp
    • Priority: 10
    • Weight: 10

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Step 3: Configure Termination

Termination defines how Rounded can send calls via Twilio.

  1. Go to the Termination tab
  2. Note the displayed Termination URI (e.g., your-trunk.pstn.twilio.com)

  1. Configure authentication (choose one method):
  1. Click + next to IP Access Control Lists
  2. Create a new Access Control List:

  • Friendly Name: “Rounded ACL”
  • CIDR Network Address: Contact team@callrounded.com for Rounded IPs

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Method B: Credential Lists

  1. Click + next to Credential Lists
  2. Create new credentials:

  • Friendly Name: “Rounded Credentials”
  • Username: Choose a username
  • Password: Generate a secure password

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Step 4: Associate your numbers

  1. Go to Numbers tab in your SIP Trunk

  1. If you don’t have numbers yet, click Add a number > Buy a Number
  2. Or go to Phone Numbers > Manage > Active numbers
  3. Select the number you want to connect
  4. In the number configuration:
    • A call comes in: Select “SIP Trunk”
    • Choose your previously created trunk

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Step 5: General Settings (Optional)

Configure additional trunk settings in the General tab:

Key settings to review:

  • Friendly name: Descriptive name for your trunk
  • Call Recording: Enable if needed
  • Secure Trunking: Enable for TLS/SRTP
  • Call Transfer (SIP REFER): Enable for call transfers

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Step 6: Configuration in Rounded

In the Rounded interface, configure your SIP trunk:

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Number settings

  • Phone number: Your Twilio number (e.g., +15551234567)
  • Friendly name: “My Twilio number”

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SIP Trunk settings

  • Termination URI: your-trunk.pstn.twilio.com (from step 3)
  • Username: Leave empty (optional)
  • Password: Leave empty (optional)

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Step 7: Test the configuration

  1. In Rounded, create a simple voice agent
  2. Assign it to your Twilio number
  3. Test:
    • Inbound call: Call your Twilio number
    • Outbound call: Initiate a call from your agent

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Troubleshooting

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”403 Forbidden” error

  • Check that the origination URI is correctly configured
  • Make sure the trunk is active

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Inbound calls don’t work

  • Verify that the number is properly associated with the SIP trunk
  • Check the webhook configuration in Twilio

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Degraded audio quality

  • Check your internet connection
  • Test with UDP protocol if TCP is problematic

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Pricing

Twilio charges:

  • Inbound calls according to your plan
  • Outbound calls at Twilio international rates
  • Monthly fees for the SIP trunk (consult Twilio pricing)

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Support

For help:

⚠️ Important: Always test your configuration with non-critical calls before going into production.