Roger Mills formulated the question :
Does that include Withheld? If so, I hope you never need to receive a call
from a hospital or doctor's surgery because they invariably withhold their
numbers.

With my trueCall unit, such calls can still get through as long as the caller
says something when asked to identify themselves.

No number, no get through. We have had calls from the doctors surgery
and yes it was witheld, they quickly realised and used a none withheld
number to ring.