Telco selective call blocking is best answer. Only the Telco knows the I.D. of the incoming call before it generates ring voltage on your phone line. In order for an aftermarket device to do what you want, you would have to hear at least one ring, because the caller I.D. information is sent in digital format between the 1st and 2nd ring. So, an aftermarket device would have to process all 1st rings thru the unit, or, all first rings would go thru to all house phones. Either option is not very marketable.