Calls like this are what makes Caller ID something I can't live without.
If it's a number I don't recognize, I simply don't answer. If it's important enough, they can leave a message, and I can choose whether or not to call back. If I do call back, I use a number I know and trust, not just any old number they leave on voice mail. The only exception is if it were someone needing my help that I know.
99% of important calls, I already know what they're about. The other 1%, they'll call back if it's important enough, or, if it wasn't, where's the harm in not answering a call, what am I losing? I am no worse off than I was before the call was made.
Some "old-fashioned" people seem to want to answer the phone no matter what number it is, just in case it's "important." Well, they also seem to be the same people that either get caught up with crooks, or at the very least give crooks a reason to keep bothering them.
Call me paranoid, but I think that's just the way it is in this day and age. I don't think too many people would disagree with this either.
Sorry to be off-topic, but I think it's kinda relevant to this thread, but please know that I am by no means giving a lecture, I'm just stating my opinion.