Download the "Disconnect Ring Tone" and play it whenever you get a call such as this. Note there is a pause between your picking up your phone before someone answers. This is the computer determining whether it has reached a valid number. If you play the disconnect tone, the computer automatically removes you from their calling directory.
PLEASE COME TO MY HOME AND SHOW ME THE SIGN YOU WANT TO PUT UP ON MY FRONT LAWN I WOULD LOVE TO MEET YOU IN PERSON, EVEN IF ONLY FOR 5-SECONDS. I HOPE YOU ENJOY EATING SPAM, LOTS OF IT!!!!!!!!!!!!!!
When they call me at work, I press whatever number saying 'i would like to learn more / talk to them." THen when they answer, I tell them to 'please hold for one minute' - and then put them on speaker, and walk away and talk about them with my co workers.