How will this be implemented from a technology and policy perspective?

The idea is one I am definitely supportive of. My phone rarely comes out of DnD now because of the robocallers.

But the devil is in the details. Forcing people to add someone to their contact list before being able to receive calls from them will probably be a bit draconian.

Another possible solution would be that someone can request access to call you and there is some service that verifies their identity and presents that information to you.

"[NAME] is requesting permission to contact you through [VOICE CALLS, EMAIL, TEXT]. Allow/Deny?"

Another good solution might be to add something equivalent to HTTPS / SSL certs, where only secure and verified identities can contact you.