And this is one of those times.
Remember: the national Do Not Call Registry is your friend. Register your telephone numbers. Only use the ".gov" domain for doing stuff like that. For instance, if you're my parents, click on the link above and follow the instructions. You can add your home and cell phone numbers all at once.
Note that you will get a separate email for each phone number you enter, asking that you confirm. Make sure you click on the link in each email confirmation (and make sure the emails don't end up in your spam folder like they did with me.)