What I find especially strange about the discussion how this will not work is that in many places it just works. Where I live, robocalling can easily be non-existant if you don't want it, simply because a party that contacts your phone is fined and if the telco cannot identify that party they carry the fine.
There is a legally binding preemptive register for cold callers, and a formal right to refuse to be contacted by parties you have corresponded with in the past. I've seen it work when two years ago I a bought a spare sim-card, and forgot to block that number. It saw about five attempts in a couple of days (obviously junk as I never actually used the number) before I blocked it. No more garbage calls since then.
