I just received a call at my home number from some company that didn't bother to explain why it was calling, nor did it indicate any means of getting myself removed from its calling list. The message basically said, "This is not a sales call; please don't hang up. We have a very important message for you. Please return our call to 770.524.8767 or toll-free 1.800.456.4601."
I went ahead and called from a phone here at work, and was connected to someone. "Hi; you just left a message on my machine and I'd like to know what's going on."
She replied, "Can you give me the number we called?"
"I don't feel comfortable giving you that information."
I just reported them to the FTC