We have been using Twilio as our telecom provider but have switched to a BYO SIP Trunk for our main outbound dialing. I'm now being told that Warm Transfers are not available. Can anyone offer any advice on to how we can do this and if it is in fact possible?

Warm transfer functionality is currently only available with Twilio-based telephony systems. For BYO SIP Trunk, you can use SIP REFER to transfer calls, but this does not provide the full warm transfer experience. Here’s a sample configuration for a SIP REFER transfer:

json
{
  "type": "transferCall",
  "destinations": [
    {
      "type": "sip",
      "sipUri": "sip:15557654321@sip.your-provider.com"
    }
  ]
}

For more details, see the [Vapi call forwarding documentation](https://docs.vapi.ai/call-forwarding). Source: - [Call Forwarding](https://docs.vapi.ai/call-forwarding)

Hi, The warm-transfer-say-summary mode (and other basic warm transfer modes) are Twilio-only features and do not work with SIP-based telephony. For SIP setups, we recommend switching to

warm-transfer-experimental

mode. This mode works with both Twilio and SIP providers, as it uses the assistant’s own TTS engine (instead of Twilio’s built-in speech) to deliver the summary to the operator.