Do Not Call Registry, run by the Federal Trade Commission.
Input up to three phone numbers (or call 1-888-382-1222) to stop telemarketing calls. You can register both landline and cell phones. If you have more than three numbers, you can come back to the site and input the others. You'll get email confirmations for each one.
Did you register once but want to double-check that your number is still there? There is good news: Numbers on the registry do not expire. So chances are your number is still there, but there is a link to make sure. If you move or get a new number, it's not a bad idea to make sure that new number is registered.
Click "More Information" then "Information for Consumers" to get the FAQs.
Everything on the site, including the FAQs, are available in Spanish.