Call blocker might be of some help. Also don't pick up on numbers you do not recognize, or where there are caller IDs that seem odd. Or where there is no caller ID.
Yeah, this was stern-sounding "Alex Thompson" from the "National Police and Troopers Association" asking for contributions. With these folks and their ilk, I like to ask what they do with the contributions (more often than not, they fumble around looking for the cheat-sheet to read from, then give some canned speil...) and waste some of their time. Ultimately, I pledge a modest amount to be paid by check when I receive their invoice by mail...sure I will...
Unfortunately, the National Do-Not-Call Registry allows calls from nonprofit organizations, but did you know that there are over 1.4 million non-profits in the U.S.? Let's see, if each of them called everybody, no one would do much of anything except answer the ringing phone...