It's not that simple. Radio works fine. I think voice messages are a horrible match for the phone system for some reason -- maybe because we're conditioned to talking to a hand-set means synchronous communication.

Maybe it'd be an intersting experiment to have a group of people go into one of two booths -- one with a smart phone/hand set -- one rigged like a recording studio -- and ask them to record an imaginary message to "... eg: a family member" -- and see how/if the messages differed?

Also see my comment up-thread about snail mail and cassette tapes.