You make yourself available by phone and internet so you can contact people and be contacted.
If you want to restrict those people who contact you by phone or internet you take steps to try and prevent them.
I have a phone that will only allow people in my contacts list to dial straight through OR announce who they are so I can decide if I want to speak to them. If they don't announce they don't get through.
What you have to consider is that how can a phone company decide if the person calling you is a bona fide caller that is not in your contacts list or a junk caller?