How a warm transfer works when the receptionist is an AI
A cold transfer is easy: the agent says "one moment" and the call jumps to another number. A warm transfer is what a good receptionist does instead. She puts you on hold, calls her colleague, tells him in one sentence who is waiting and why, and only then connects you. You never repeat yourself. We wanted the AI to do exactly that, and it turned out to be the most detailed piece of engineering in the product.
Step one: hold, honestly
The agent says the hold line once, in its own language: "One moment, I will get my colleague." Then music plays. The caller's microphone is muted from the agent's point of view, so the conversation does not continue while the caller thinks nobody is listening. That mute was a one-way door in an early version; the caller came back to an agent that could not hear them. It is fixed, and it is why we test on real phones.
Step two: dial the colleague into the same call
The colleague's phone rings. When it is answered, they join the same call the caller is in, but they cannot hear each other yet. The agent talks to the colleague privately: "Hi Jonas, I have Sara on the line about a renewal. She wants to move to the yearly plan. Ready?" The briefing text is yours to change, and it is spoken in the agent's language.
Step three: connect, and leave quietly
When the colleague says yes, the agent connects the two and stops speaking. From here on it is a normal phone call between two people. There is one recording of the whole thing, including the private consult, because one phone call is one call.
What if the colleague is a voicemail?
This is the part that separates a demo from a product. Phones are answered by voicemails, by "the number you have dialled", by a colleague who picks up and says "sorry, in a meeting". The agent listens to what answered and tells the difference between a person and a recording. If it is not a person, or the person declines, the agent goes back to the caller, says so, and offers what it can: a callback, a message, another colleague. It never hangs up on the caller because a transfer failed, and it never says "you are connected" before you actually are. That last sentence was a real bug, and the reason there is a check for it.
Why it matters
Callers forgive a machine for not knowing something. They do not forgive being dropped. A warm transfer that always lands somewhere is the difference between an agent your customers tolerate and one they thank.