Connecting a Custom Phone Number via SIP Trunking (e.g. providers include Twilio, Telnyx, Vonage, Zadarma, Exotel)

You can connect your existing phone numbers to Retell AI using SIP trunking. This guide walks you through the setup process and common troubleshooting steps.

Setting Up SIP Trunking

1. Navigate to the Phone Numbers tab in your dashboard

2. Click Add

3. Select Connect to your number via SIP trunking

4. Fill out the required fields:

   • Phone Number: Enter in E.164 format (e.g., +12025551234)

   • Termination URI: Use the full URI provided by Retell AI (e.g., example.sip.livekit.cloud)

   • SIP Trunk Username: Enter the provided username

   • Password: Enter the provided password

SIP Provider Configuration

For more detailed instructions on configuring Elastic SIP trunking with your SIP provider (like Twilio, Telnyx, Vonage, Zadarma, Exotel): visit our Custom Telephony Overview documentation.

Common FAQ:

• Will it throw errors if the details or configuration is incorrect?

  No, Retell will not be able to know if the setup you provide works or not until a call is made.

• My inbound call is not connecting, what should I do?

  Please check your origination setting in your SIP trunking provider. Also check the logs in your telephony provider, and perhaps open a ticket with them.

• My outbound call is not connecting, what should I do?

  Please check your termination setting in your SIP trunking provider, and make sure you provide the right termination url to Retell. Also check the logs in your telephony provider, and perhaps open a ticket with them.

• Will I be able to transfer call using SIP trunking?

  Yes you can use the transfer call feature with SIP trunking. Please note that if you intend to use SIP REFER (cold transfer with the transferee’s number), you will need to configure that in your SIP trunking provider to allow SIP REFER and PSTN transfer, with the transferee’s number showing as caller id.

• Will I be able to press digit using SIP trunking?

  Yes, you can.

• I need to change the configuration of the imported number, how can I do that?

  Right now you’d need to delete and re-import the number.