Do you find that you get problems with phone calls? No, not the usual horrible service that you get from your call plan provider. No, rather, do people phone you and just breath down the line at you? Do you get dropped or missed calls? People who won't leave a meassage?
You can find out who they are now thanks to an interesting little website. CallerBase allows you to look up any number that your caller ID has captured and find out who they are and where they are.
The basic service is free on the CallerBase website and there's paid for services possible for unlisted and cell phone numbers. If you're being troubled by these types of calls then it looks like a great service to help you.