Use Google Voice. Other than close friends/relatives...give out the Google Voice # which is what i always do. Filtered automatically. Shoot...i even give it out to friends too...never know where your # ends up these days.

I call forward all my landline calls to my google voice number so I can choose to block certain calls, then next time a blocked caller calls, they get the message "Number no longer in Service"!

You can buy sentry from Amazon. It saves you all calls, except that you like.

How do you do that?

I recently purchased and installed the Sentry 2 call screener/blocker for my landline.  Fantastic! After using the conventional "blacklist" blocker device for years, I now feel I have fully retaken control of my private land-line phone, have peace and quite and have finally defeated those dirt-bag scammers and telemarketers!  The problem with the conventional call blockers is that the scum callers keep changing their fake caller ID numbers so they can get around the blacklist blockers.  The Sentry 2 device is another level of protection.  It can be found on Amazon or Ebay -- check it out.  (I am not affiliated with any company that makes or sells Sentry 2 -- just a very, very satisfied customer who want's to share my success story).  :)