I’m trying to build a warm-transfer / three-way bridge flow using Retell AI + Twilio + n8n. I have tried multiple ways of conference calling but there seems to be some limitation to retell or twilio that stops me from completing it
The goal is:
A caller is speaking with a Retell AI agent. When the AI determines the caller should be connected to a live representative, I do not want the caller to hear normal ringing, dead air, or a standard hold/transfer experience. I want the AI experience to stay conversational while the representative is being dialed in the background.
The ideal flow would be:
Caller is on an active call with the AI agent.
AI triggers a custom function/webhook instead of using a standard transfer tool.
n8n receives the webhook and starts the transfer orchestration.
Twilio dials the live representative in the background.
While the rep is being dialed, the caller should continue hearing the AI, not ringing or hold music.
When the representative answers, the rep should be joined into the same live call/conference.
The AI should hear that the rep has joined, give a short handoff like:
“I have John Smith on the line. The best callback number is 555-123-4567. Please take it from here.”
After the handoff, the AI leg should disconnect, leaving the caller and representative connected.
The main challenge:
Retell’s standard transfer behavior appears to interrupt the AI session or causes the caller to hear ringing/hold behavior. I’m trying to avoid that by using Twilio Programmable Voice / Conference logic instead of a normal transfer.if someone has done this before we will pay to build
The closest built-in solution for what you want is the Warm Transfer feature on the Transfer Call tool — not a custom Twilio conference flow.
Key capabilities that match your goals:
On-hold music: configurable audio played to the caller while the rep is being dialed (replaces ringing). The doc notes the default is a ringtone, but you can set custom audio.
Whisper message: spoken privately to the rep only (your “John Smith / callback 555-…” handoff).
Three-way message: spoken to both parties once connected.
Human detection + agent detection timeout: ensures the caller is only bridged when a real human picks up.
Custom SIP headers and caller ID override (Twilio supports user’s-number override on warm transfer).
While the rep is being dialed the caller hears the on-hold audio — the AI staying conversational with the caller during the dial is not a documented behavior. After the three-way intro, the AI leg drops, leaving caller + rep connected, which matches your last step.
If the built-in warm transfer is failing for you, see the debug guide ( Debug call transfer failure - Retell AI ) . You can also trigger this via a custom function instead of the standard tool, but the underlying transfer mechanics (SIP DIAL, hold audio, whisper, three-way) are what Retell exposes.
I have been tasked to make it happen without any hold time inbetween. The only way that I can tell this can be accomplished it to do it using a custom twilio conference room. We have presented all of the options you have and they said it wasnt good enough. I was hoping someone has overcome this before.