Mobile phone: If I don't know the number, they go to a voicemail-to-text service. I get to read the text and choose whether or not to call them back. Land-Line

Mobile phone: If I don't know the number, they go to a voicemail-to-text service. I get to read the text and choose whether or not to call them back. Land-Line: Answering machine contains just 'This line not active' set of tones plus a terse 'Leave a Message' audio. The robo-callers hear the tones and hang up. The humans hear the 'Leave a Message' and have to choose between hanging up immediately or leaving a message. I get to choose whether I feel like calling them back.