Call came in on our landline number, Caller ID showed "Unknown Caller" and they left no voicemail. Since we never answer calls from un-familiar numbers and if they leave no voice mail we normally block the number. Our call blocker unit will hold 1500 numbers. We have not used even 1/3 of the unit's capacity and the number of bogus/suspicious calls have dropped from 10-12 per day to 1-3, some days ZERO.