Cold transfer
A cold transfer is a call handoff that sends an active caller directly to another person, number, or endpoint without first briefing the recipient or confirming that the recipient will answer.
The transfer begins after the original agent chooses a destination. The phone system routes the caller to that destination, and the original agent leaves the conversation. The caller may reach a person, a ringing line, voicemail, or a failure message depending on the destination and its availability.
This makes a cold transfer different from a warm transfer. A warm transfer keeps the caller waiting while the agent contacts the recipient privately, shares context, and connects the parties only after acceptance. A cold transfer removes that consultation step. It is faster and simpler, but it gives the original agent less control over the outcome.
For an AI phone agent, the transfer rule should specify both when to transfer and where to send the caller. Useful triggers include an explicit request for a person, a task outside the agent's scope, a policy restriction, or a situation that requires specialized judgment. The destination may depend on the caller's intent, account type, language, location, or the time of the call.
Passing the audio call does not necessarily pass the information collected during the conversation. If the recipient needs the caller's name, reason for calling, or prior answers, that context must be made available through a separate system or collected again. A concise message before the transfer can also tell the caller what will happen next without implying that someone is available.
A reliable cold-transfer flow includes a fallback for no answer, busy signals, invalid destinations, and voicemail. Teams should test each route from the caller's perspective and decide whether an unsuccessful transfer should end the call, try another destination, or provide another next step.
In practice on ThunderPhone
ThunderPhone supports cold and attended warm transfers. Demo numbers and browser-based calls are limited to cold transfer. Warm transfer requires an eligible production number that can place an outbound SIP leg.