This incoming call block device was designed to block call (s) from ringing your phone. In Black list mode, this incoming call blocker device will block number (s) (up to 120 specific telephone numbers, prefixes or entire area codes). In White list mode, it will only ring your phone(s) when specific phone(s) numbers or area codes call you. This call blocker can also block "Private", "Unknown", "Out of Area" and "Anonymous" calls from callers using *67 or *68 to block their CallerID feature when calling you.