Google Voice has a feature to block callers so they don’t bother you. These blocked callers get a message of “The number you are trying to reach is no longer available. If you feel you have reached this …” with the traditional background music that makes it seem like the number is no longer available. I’ve been using this feature quite a lot. In fact I don’t answer 800 and 866 numbers and see if they leave a voice message. I block them if they are spam. If they didn’t leave a message I then look them up with http://800notes.com/Phone.aspx/ to see if they are legit or get marked as blocked spam.
Google voice unfortunately doesn’t have any way of handling phone numbers that have no caller id. So I get bothered with them. I’d love to not be bothered with people who have no caller id. Or route them to a phone I never pick up that has a voice message saying that since they have no caller id they must leave a message and that I would then call them back. Alas Google Voice needs a bit of fixing so it can handle unregistered phone numbers to my satisfaction.