This is a known gap — carrier voicemails that read numbers sound like humans, so most detectors miss them.
The issue is the assistant responding before there’s enough confidence in the transcript.
What’s worked for me is a short pre-response gate that checks early text for high digit density and cadence, then exits if matched.
Do you control the first-response logic, or is Vapi/Twilio handling that entirely?
@Jerm