I received a call from 530-405-9387, caller ID'd it as Woodland CA. It rang up until my answering machine answered. Left no message. I do not answer any phone calls unless I know the number, even anonymous and private callers go to my answering machine. I have told my friends and the places I do business to always leave a message if they call because I screen my calls.
I think you're going to find that 250 isn't enough. I have a stand alone call blocker that we haven't had for all that long and I have about 50 numbers on the white list and more than 150 on the black list.