This is List of devices to screen telephone calls.
Created by Digitone Communications is a device which allows a phone subscriber to reject all calls from numbers with a Caller ID read-out of "Out of Area, Unavailable, Private, Anonymous, Name Not Provided, Unknown, No Name at all, and no number at all". It also is possible to programmed for "wildcards" such as to blocking an entire area codes, or a specialised 80 digit blocklist that can be created by the subscriber.
Created by Privacy Technologies, Inc and uses a Special information tones built into the telephone system to trick auto-dialing equipment into believing it has reached a non-working telephone number.