Everybody on the "Do Not Call" list should be asked to approve this first.
After I've been on the Do Not Call List, I have to tell them I Do Not Want to Be Called? Duh.
Then they would have to call everyone on the "Do Not Call" list for permission. But they can't call those listed on the "Do Not Call" list, because they are on the "Do Not Call" list!
What's a slimeball telemarketer to do?