From day by day we know more about new version of Android which name will this time start with the letter P. Some Sony workers found in source code of new AOSP information about potential new feature which will help us with unwanted calls at uncomfortable moments.
Android P will have option of blocking all incoming calls made from numbers which aren't on our list of contacts. Option will have also other criteria - we will have opportunity to block private numbers, pay phones or calls which aren't showing us any information about caller. Whole feature will be disabled automatically when we will make emergency call (for example 911 number). New option looks interesting, but it's not sure that Google has enough time to add this feature to the newest version of Android system.