Northern Telecom Meridian M5316 business telephone

I've learned a lot of cool things at my new job, both related to the work I'm doing, and incidental things which I research myself. One example of the latter is the working of business telephone systems, which I've never been up close and personal with until now. In particular, I've taken quite an interest in Northern Telecom, both in their history as a company, and in the residential and business telephones they made.
This video concerns the Nortel product I've taken the most interest in, the Meridian series of digital business telephones. In this video, which takes place in a conference room at work, I give a brief history of Nortel, and we explore, and demonstrate in a call, a Meridian M5316 centrex telephone.
The methodology by which most business phones work is called a Private Branch Extension, or PBX. A PBX may have one or more standard telephone lines coming in, and distributes calls to one of multiple phones in the building. In the case of most phones, the phones communicate with the PBX digitally. PBX's can provide such abilities as storing voicemail locally, calling from one local phone to another without having to use an outside line, and paging, whereby your voice comes through the loudspeaker of every phone, like an intercom system. If you've ever been in a store and heard a loud, sharp DTMF tone preceding a page, that's a Nortel system at work.
KZbin user Retrochad has a video demonstrating a Northen Telecom Norstar system. The Norstar is a similar, smaller system that can service up to a few dozen phones, as opposed to a Meridian system, which can handle tens of thousands of phones.
• Northern Telecom Norst...
This fan of Northern Telecom equipment has a blog where he posts lots of pictures of Nortel equipment he sees still in use out in the wild. He has his own Norstar system running in his home.
blog.squarebabo...
This creative and well-written Northern Telecom film from the late 1980s introduces the Meridian system:
• Northern Telecom Merid...