Logic of SIP call routing for Retell AI + Jambonz.cloud (dynamic number substitution)

Call SIP Routing Logic for Retell AI + Jambonz.cloud (Dynamic Number Replacement)
Brief Description

I have built (already ready) an outbound calling system using Retell AI.
The flow works as follows:

• n8n initiates a call to Retell

• Retell makes the call through Jambonz.cloud (important: this is a cloud application, not a self-hosted instance)

• Jambonz then sends the call to the local telecom operator

• Jambonz is needed because Retell uses elastic SIP trunking, while the local operator does not

Now I need to add additional routing logic between Jambonz and the operator:

What Needs to Be Implemented

1. Dynamic Call Routing Based on Metadata

• Retell can pass a custom SIP header with metadata

• For one specific destination number, it is necessary to:

  • extract the target number from this metadata

  • replace the original dialed number with the extracted one

  • then perform the usual call routing

• All other calls should go through unchanged

2. Additional Conditional Rule

• If a certain tag is present in the metadata:

  • the number replacement should be as follows: prefix (from metadata) + original subscriber number

Current Configuration

• Outbound Assistant Retell AI

• Jambonz.cloud

• Local SIP Operator (not elastic)

What Is Required from You

• Analyze the current architecture and advise where it is better to implement the logic: through Jambonz (task, hook, app) or through a separate webhook server

• Implement a simple handler (Node.js or Python) that:

  • accepts SIP headers

  • applies routing and number replacement rules

  • returns the updated destination number

• Ensure that this logic applies only to one specific number, while all other calls go through unchanged

Required Skills

• Strong experience with Jambonz (preferably cloud version)

• SIP telephony, SIP headers, routing logic

• Webhook/API development (Node.js or Python)

• Experience integrating with Retell AI will be a plus