Comment Callback (Score 1) 216
Simple and already exists, the first time a number is seen the caller gets a machine asking them to leave a message, this then gets forwarded to the recipient who can choose to take the call or not based on the message.
Once the call is taken the number is whitelisted and the caller gets through first time the next time.
Once the call is taken the number is whitelisted and the caller gets through first time the next time.