This is a seriously useful feature for Android. My last phone was running 4.4.2 and it had this feature. Now that I am on the bleeding edge of Android, the feature seems to be gone. Worse yet, I have tried 5 different Contact whitelist apps and not a single one blocks calls properly.
I get 5+ scam calls a day and all I can do is just pull the phone out of my pocket, see the random number and swipe the call away to stop the vibrating.