The National Do Not Call Registry is a US government listing of phone numbers that telemarketers are forbidden to call. I'd forgotten about this; the registration only lasts for 5 years, and if you signed up the day it came out, like me, it will be expiring soon. The good news is, you can go ahead and re-register early and stay active on the list. Here is the registration page;
National Do Not Call Registry
National Do Not Call Registry