Move Retell AI telephony to Bird

Keep the Retell AI agent runtime while moving its telephone connection to Bird. Test each direction and the customer conversation separately.

1. Choose what is moving

Decide whether you are retaining Retell AI as the conversational runtime. This guide moves its telephone connection to Bird; it does not claim to copy or replace the runtime’s prompts, models or tools.

2. Prepare the Bird trunk

Create a trunk and enable the required direction. For incoming calls, configure the runtime’s documented delivery gateway. For outgoing calls, use the Bird SIP domain and an allowed authentication method.

3. Connect the runtime

Use Retell’s SIP setup and number import contract for its side. Configure each direction independently:

Direction	Bird configuration	Retell configuration
Customer calls your number	Enable inbound, select the trunk on the number and configure a delivery gateway.	Import the same number and assign its inbound agent; use Retell’s published SIP destination for the Bird gateway.
Agent calls a customer	Enable outbound, allow a Voice-write API key and verify the caller ID.	Set the imported number’s termination host to the Bird trunk domain, with digest username bird and the allowed key secret.

For a new Retell number import, the request body below connects a tested Bird trunk and an existing Retell agent. Replace every placeholder, then submit it to Retell’s POST https://api.retellai.com/import-phone-number using your Retell bearer key. Inspect an existing import before creating another one.

Code example

{
  "phone_number": "YOUR_E164_NUMBER",
  "termination_uri": "YOUR_BIRD_TRUNK_DOMAIN",
  "sip_trunk_auth_username": "bird",
  "sip_trunk_auth_password": "YOUR_ALLOWED_BIRD_KEY_SECRET",
  "transport": "TLS",
  "inbound_agents": [{ "agent_id": "YOUR_RETELL_AGENT_ID", "weight": 1 }],
  "outbound_agents": [{ "agent_id": "YOUR_RETELL_AGENT_ID", "weight": 1 }]
}

Keep credentials in the runtime’s protected configuration. Importing a number configures Retell; it does not port the number or change its Bird inbound route. Preserve the E.164 caller identity separately from the digest username. Configure compatible media settings and retain your current production route until both directions have passed a real call test.

First prove the Bird trunk with the terminal quickstart. Set the caller ID, destination and credential variables from that guide. This places a real call through the trunk without relying on the agent runtime:

Code example

bird voice tools test-call "$VOICE_TO" \
  --trunk "$BIRD_TRUNK_ID" \
  --caller-id "$BIRD_CALLER_ID" \
  --protocol tls \
  --duration 30s

bird voice list

Keep provider runtime sessions and Bird call IDs as separate references. The external runtime’s create-call operation is not a Bird SDK method, and a trunk ID cannot replace an agent ID. Test routing and two-way audio first, then the runtime’s actual tool calls, interruptions and human handoff.

Related resources

Continue with the documentation, guides and examples for this topic. Resources are in English.

Understand the conceptWhat is a voice API?Explore the capabilityVoice Implementation guideVoice overview

Get an implementation brief

Move Retell AI telephony to Bird

1. Choose what is moving

2. Prepare the Bird trunk

3. Connect the runtime

4. Route a controlled test

5. Move production numbers deliberately

References and next steps

Related resources