Sounds like a recipe for disaster, says
Torben University
+49 1234567890
notreal@not.gmail.com
who now gets tons of scams and cold calls.
But I guess you were joking a little, by now? Anything real would need to be powered by telcos... not very encouraging from a privacy perspective.
And improving on this devolves into a cat-and-mouse game like iCloud Private Relay, right?
Still would be an additional layer of obscurity for apps that try to coerce users into sharing contacts.
But even then, there must be enough people using the fake contacts, otherwise it's just a more precise fingerprint than not sharing at all.
Thinking about it.. we're not far away from apps requiring you to share your "verified contacts" -_-