I won't pick up any unknown caller IDs and I let the answering machine deal with it. If it is a friend trying to reach me, they can leave a voicemail. For the past two months, an unknown number with same area code has been calling my home phone every day, at different times of the day - but never leaving a message. Same caller ID. Reverse phone lookup doesn't flag it as malicious (scam, telemarketer) but scammers have been notorious for caller ID spoofing. Scam artists do not care when you tell them they have reached an unpublished phone number. By calling at different times of the day, they are trying to identify a time window when a live person is there. Unpublished phone numbers are no longer a good solution.
I plan on building my retirement home soon, and I am looking into ways to protect my phone number (like prefixing the SIT right before the greeting message) to keep these scum away.