Under Admin → Blacklist → Settings, you can enable ‘Block Unknown/Blocked Caller ID’. However, it looks like it only blocks caller ID numbers that show as ‘Unknown’ or ‘Unavailable’ and it is case sensitive, so ‘unavailable’ will not get blocked.
I submitted a feature request with a PR that fixes the case sensitive issue and blocks when matching the following caller IDs:
unknown
unavailable
anonymous
private
restricted
blocked
Please raise your voice if you have any questions or concerns
Another thing that would be nice (I don’t know that it would be an easy addition though) is split routing for “Blacklisted Numbers” vs unknown, anonymous, etc.
A good example we block scammers and pushy salespeople that don’t understand the word NO. Currently our blacklist sends them to a dedicated voicemail. With this change to allow for the few legitimate customers whose numbers come up anonymous I would need to route the blacklist to a confirmation IVR instead.