They're toll-free calls. They don't cost anything to the caller. You can also send a text-message as a vote, which MAY cost the cell phone user - depending on the cellular plan. Some people have a flat fee for all text messaging - especially if you have teenagers.

Last year, AI had more votes than viewers generally. If I recall, they had 30-40 million viewers, but over 50 million votes on more than one occasion.