My cell phone has a "Do not disturb" mode where it won't ring except for caller IDs in my contact list. So family and friends get through, but spammers go direct to voicemail.
These days you can get answering machines with a whitelist feature. Don't bother with blacklist, spammers just randomly change numbers.
My Panasonic phone has a set up where someone calls but the phone won’t allow the caller to ring through unless they follow the .. “If you wish to talk to the person you are calling, press the # button.”
(Or any other button or combo of numbers you want)
Great System!
You never hear the spam calls ringing through!