I've been using email at work since 1982 (OK, that's because I work in a large scientific lab which always had good access to the Internet and its various precursors). In those days I remember being thought a bit strange when I tried to explain to people outside why it was better than fax. Now at work we still use it, much too much perhaps. The funny thing is that almost nobody uses IM or SMS despite their availability. I think this is true in most scientific labs. I suspect that's mainly because it allows you to wait before replying and the sender can't usually see whether you are there at your computer to see his misive or not.
Back in the late 1980s a few of us did use an early form of instant messaging which worked intercontinentally. That was the TELL command on IBM's VM/CMS mainframe systems.