A phone line usually starts with one AI agent that greets callers and works out what they need. Many calls then move into territory where a different agent is better prepared: billing, scheduling, a specific product line, collections. HellouOne AI voice agents can now pass a live call to another AI agent in the same account. The call moves to the agent best suited to the next part of the conversation, and the caller stays on the line the whole time.
This post is for teams that run several AI voice agents and want each one to stay focused on what it does best, instead of building one agent that has to know everything.
Why one AI agent is not always enough on the phone
An AI agent that answers every kind of question needs long instructions and a large knowledge base, and it gets harder to test and improve over time. Splitting the work across several agents keeps each one simple: a front-desk agent that identifies the caller and the reason for the call, and specialist agents that each own one topic with their own instructions and knowledge.
Until now, the only way out of an AI call was a transfer to people or to a phone number. With AI agent to AI agent hand-off, the front-desk agent can send the caller straight to the specialist, and a person only gets involved when the call really needs one.
What happens during a hand-off
The AI agent on the call sees the other AI agents it is allowed to hand calls to, each described by its own description, and decides when one of them is the better fit.
The call is passed to the target agent over the phone system, while the caller stays connected.
The agent that takes over does not repeat the normal greeting. It says one short takeover line and continues from where the conversation was.
It receives a short context note from the first agent, so the caller does not have to explain everything again.
The call stays one conversation in the line's inbox, and a private note records the hand-off for your team.
If the hand-off does not go through
Sometimes a hand-off cannot complete, for example when the target agent is not available. In that case the AI agent that tried the hand-off takes the caller back and keeps helping, so the conversation continues with an agent that already knows the context. If that also fails, the line's main AI agent gets one try to pick up the call.
How this works in HellouOne
Hand-offs are set per phone line. On each AI phone line, the AI agent hand-off toggle opens the list of AI agents that line can pass calls to. Only administrators can edit that list. The line's own main agent cannot be on it, and you can pause an entry to stop hand-offs to that agent on the line without removing it.
Every AI agent on a hand-off list gets an internal extension, which the platform assigns and manages for you. You can see it, read-only, on the agent's Voice tab, which shows an empty state while the agent has no extension. There is nothing to dial or type by hand.
In the call history, each part of a handed-off call is its own call record, linked to the first one, and the call detail shows the legs. A leg that started with a hand-off is marked as handed over from another AI agent. This sits in the same call history for phone, WhatsApp and AI calls your team already uses.
Reports count a handed-off call once, and a hand-off between AI agents is not counted as an escalation or a transfer to a person.
AI minutes are measured per leg, summed and rounded once for the whole call, so a hand-off never adds billed seconds.
For developers, call records in the HellouOne API now include parent_call_id, which points to the first leg, and ai_transfer_hop, which tells you which hand-off started a leg.
Tips for a smooth setup
Write a clear description for each specialist agent. It is what the agent on the call reads when it decides where the caller should go.
Keep each line's hand-off list short and focused, so the choice is easy and predictable.
Keep the human route in place for cases an AI agent should not handle. Hand-offs between AI agents work next to it, not instead of it.
Review a few handed-off calls in the call detail after the first days, and adjust descriptions where callers landed with the wrong agent.
If you are starting with voice, the AI voice agents page explains how HellouOne answers and places calls, and the voice plans show how AI minutes are included. A team of focused AI agents that pass calls between them gives callers one continuous conversation, and gives you agents that are easier to build, test and improve.
