When caller ID shows anything but a number or person I know, I pick up and immediately hang up.  If I am busy I just let the answering machine handle it.  It says, "We screen all calls. You may leave a message."  They never leave a message - so, it is basically a non-problem. :)

A woman who sounded like she was 100 years old called from this number, asked for me by name, and said she was calling on behalf of the College Republicans. Hilarious. Wanted me to take a "confidential survey" about "education in Tennessee." Last time I got one of these calls I was switched to a recording with Newt Gingrich's voice. Considering I am a liberal, progressive Democrat with an unlisted phone number I find it very suspicious that the TN GOP has somehow got my personal phone number. Someone has sold my info to a political organization and I'm very ticked off.