Answer an inbound call on a Mentium number routed to a native provider.

Admission — which agent owns the number, Highway screening, the MyCarrierPackets pre-call lookup, the call record and the caller-specific prompt — is the same code the ElevenLabs conversation-init webhook runs, so a number behaves identically whichever provider picks up. The rendered prompt is stored on the call's metadata because, unlike ElevenLabs, there is no init response to carry it in: the WebSocket reads it back when it opens.