Warm Transfer

A warm transfer is a call handoff in which the transferring party — increasingly, a voice AI agent — speaks with the receiving human agent before connecting the caller, passing along who is calling, what they need, and what has already happened. The caller is typically held briefly while the AI briefs the human; once the human accepts, the caller is bridged in and the AI drops off. This contrasts with a cold (blind) transfer, where the call is simply redirected and the caller starts over from “how can I help you?”

At the protocol level, warm transfers are implemented over SIP either by bridging a second outbound leg (the platform holds both calls and joins them) or via attended-transfer signaling (SIP REFER after a consultation leg). The mechanics matter for billing: on some platforms the AI’s per-minute meter keeps running for the entire bridged human conversation, long after the AI’s work ended — a hidden cost worth confirming before launch.

Why it matters for voice agents

Escalation is where voice AI deployments are won or lost. No agent handles 100% of calls, and the experience of the handoff determines whether automation feels like a service upgrade or an obstacle course. A warm transfer means the customer never repeats their account number, their problem, or the troubleshooting they already did — the single most-cited frustration with traditional IVR escalation.

For the AI side, a good warm transfer involves more than dialing: the agent must summarize the conversation accurately for the human (or push it into the CRM/ticket), select the right destination based on intent, handle the no-answer case gracefully (queue, voicemail, callback offer), and time the handoff naturally. In outbound use cases — lead qualification, appointment confirmation — warm transfer is the conversion event: the AI qualifies the prospect and warm-transfers live interest to a closer within seconds, while intent is hot.

When evaluating platforms, test transfers to your real queues and DID destinations, confirm context actually arrives with the call, and ask explicitly how transfer time is billed.

Related terms

• SIP Trunking — the signaling layer transfers run on
• DID Number — transfer destinations and caller ID
• Barge-in — natural interruption before escalation is needed