Telemarketers Listings

I always wonder how to remove myself from a telemarketers listings. My phone always ring from telemarketers. Sometimes it gets irritating especially when I'm busy doing something very important. I usually answer the phone politely, even though my mood and my nerves wants to scream already. I understand that telemarketers are just doing their job, so I answer the phone politely and respectfully ask them to put my name and phone number on their "do not call" list as I am not interested. I am not sure, but I think some of them are still calling. Now I'm thinking of having my number unlisted since many telemarketers build their lists from the phone book.