Whitelists works fine. Pin "extensions" work fine. The next step is probably just a simple question/answer regarding personal information about the recipient.

Whitelists works fine. Pin "extensions" work fine. The next step is probably just a simple question/answer regarding personal information about the recipient. Just like account security questions. Provide drop down selector/s for users to select their question. I'm not going to provide my public number here, but if a caller of mine isn't whitelisted I just prompt them for my billing zip code. Now, that's not going to work for every one, but considering who I want to get phone calls from, it's pretty foolproof. Keep the energy up @davidajackson. I'd love to see you hugely successful with your efforts!