And you can see an additional jack on the side of that plate. They were actually in existence before then for multi-line circuits, although no terribly common.

Also, the sliding plug thing that you see on that phone is basically never seen anymore. It's almost always connected via a several-inch cable now.

For the telephone geeks, the reason for all of that is that until about 1980, AT&T rented you your telephone. They didn't sell any at all, as far as I recall. (You'll see a marking on that phone that says "Bell System Property/Not For Sale".) As such, it was in their best interests to make a phone that would never break. So they were made of steel and were really exceptionally well engineered.

But now it's all commodity stuff, and those people have no interest in making a quality product. If anything, they're more interested in planned obsolescence. So there's no desire to put any engineering effort into something that (1) has a smallish user base and (2) might possibly fail before the warranty is up.