Handoff is the transfer of an active phone call from an AI assistant to a human agent — either as a warm transfer (with a short briefing whisper) or a cold transfer (raw SIP REFER). A clean handoff is what decides whether callers experience the AI entry point as helpful or as a hurdle.
Sound handoff rules are based on intent classes, escalation keywords ("lawyer", "complaint", "emergency") and confidence thresholds. Below confidence 0.6 the assistant should not guess; it should hand off. In parallel a transcript summary is pre-written into the CRM or helpdesk ticket so the human does not have to ask everything from scratch.
Technically the transfer happens via SIP REFER for classic PBX systems, via WebRTC bridges in cloud telephony, or as a callback job in a queue. Important: in a failure case (no agent available) the assistant must capture a voicemail rather than dropping the call.