Social also used to mean phoning people up, or before that writing letters (there have been plenty of famous historical friendships that were done an the speed of post).
There are still friendships that happen solely through the mail. I have a friend who is a pen pal with someone in prison. I don't know too much about prison so I don't know if there is a reason that theirs is through the mail only instead of using more modern means.
Even when I was in school the idea of a pen pal was not foreign (I was in school in the last 9 years. Is that too long ago?).
