there is a free voice mail service called youmail.com - you can assign different greetings for each number.
When ever you add a "nuisance number", they could hear "were sorry, the number you have reached has been disconnected" .....works great!
A very rude lunatic was on the other side when I answered my phone, claiming that he was with All-state Car Insurance, and claimed that I was eligible for discounted car insurance due to being a good driver, and wanted me to confirm the make of my car. I told him that I already had a car insurance and that I was not going to give any information to a lunatic that I did not know. He started raising his voice at me and I hanged up. This was the third time this I was getting a call from this number. I am going to call All-State car insurance to find out if this lunatic is representing them.