Pre mobile phones (but post caller I’d) my wife and I called each other several times a day just to say mushy things to each other. It was ok to ignore the call but an immediate second call meant “actually I need to speak with you”. I’m sure others must have invented the same system.

But I love ZipDial‘s idea to take it to another level.

The European idea to make receiving GSM calls free was brilliant. The US’s idea that “the person with the radio pays the extra fee” held back mobile adoption in the US by a decade.