Slightly different issue. In my experience, the problem tends to be from robodialers operating on behalf of scammers or fly-by-night marketing agencies. As the

Slightly different issue. In my experience, the problem tends to be from robodialers operating on behalf of scammers or fly-by-night marketing agencies. As the US phone system is currently operated, it's trivial for these kinds of actors to spoof originating phone numbers and hit every valid US phone number in sequence.