Re: It actually MAY block them depending what callback service they're using
It would be helpful if official bodies followed the general guidelines and provided a CLI number that can be called for verification purposes. My doctors' surgery and local council have modern multi-user switchboards. Both show as "Withheld" - as they are apparently unable to program a CLI of their general public number.
My other problem is having to answer "international" calls that "might" be a friend calling me.
I don't see the "Press 5 or go away" working with the usual cold callers. They are persistent beyond belief even when it is clear you are not interested from the offset.