> Heck, they haven't even exposed it unless you are a megacorp.

Cell phones surface the SHAKEN/STIR attestation status to the user via a checkmark in the telephone UI.

If you want to programmatically act on that data to filter calls... Android provides access to the attestation level via the android.telecom.CallScreeningService API. (I can't speak to what iOS provides.) For VoIP, many providers will also either pass along the attestation level in the SIP headers or by appending some text to the Caller ID string.