I've worked on a
lot of old PBXs, mostly Northern Telecom/Nortel. They went away some time ago but there are a very, very few old warhorses still in service. I was just talking to my friend who is about to retire and there is one antique mechanism still grinding away in a nearby hospital. It's a room filling bruiser of an old SL-1 NT (I think). Most of the service change dates in the thing are from
1988 when I did an upgrade on it. It's had some new stuff since but right now its sitting there in the dark humming and clicking and making dial tone and sucking up a lot of power. They make finally shut it off and if they do I told my buddy I'd meet him up there if they'd let me in, which they would. They don't really have OFF switches so somebody who knows how it works needs to render it safe.
See that IBM Selectric on the desk? Worth a few $$. I used to see them still in a lot of lawyer's offices because they still have a need. Go figure.