Altivo

Because caller ID has become unreliable in the US. It doesn't always tell you the number, or the name. Instead it gives useless things like "local call" or "out of state call" or "Indiana call." I suspect this is due to the proliferation of phone companies who are not particularly cooperative with one another and feel they owe nothing to someone else's customer.

Neither a white list nor a black list will be very effective under these circumstances.