[duncanlowe]

Not that I can add anything about the way of simulating one, but I do remember that when I was a child, my parents had such a shared line. They hated it, because the people it was shared with were quite careless and often left their phone off hook, and it was quite a way up the village to them to get them to put it back properly. Not only that, but they weren't careful about checking when the line was in use, and would regularly interrupt my parents calls. I honestly can't remember whether there was ever a non-shared line before we moved in the early seventies.