Almost 20000 people work at our site, around 10000 just on my campus. They took all our office phones away from us a couple of years ago and gave each of us a Jabra USB headset to plug into our laptop (or desktop) computer. Using Lync (now Skype for Business) as our "office phone". I believe they did the same at most of the other sites, at least the ones in North America.
At least from my perspective it has resulted in a much lower phone call volume because it is so fiddly (unless you are on the phone all the time). More IM and email, etc. which is fine with me. Only recently (with some stealth background "update") did my laptop start "ringing" through the speakers. Before that, you had to be wearing the headset to hear the "phone ring". And if you get a call during one of the enforced "work pace break" periods, the computer is locked up so you can't answer the call. Sigh. Oh well, I guess it wasn't important or they would have sent an email.
OTOH, you can place and receive calls from anywhere you are, as long as you have internet connectivity. And many people travel a lot and don't even have fixed offices (cubicles) anymore. So perhaps better for them. The conference rooms still have wired (but IP) fancy speaker phones, and there are even some vintage wall phones in places. So they must still have a few old-school phone switches.
Several years before that, they integrated the voice-mail system into Windows Exchange so messages arrive in email. For a while they even had auto voice-recognition so that you got voice-mail as text email. But with all the different languages spoken around here (and the thick accents non-native speakers have) there were some pretty amusing errors in voice-recognition, so they abandoned it. But from my perspective it was reasonably good and I was sorry they shut it off.
They also integrated Microsoft's notion of meeting scheduling into Exchange and it has been a long series of cobbled-together kludges which have never equaled the VAX-based system we had 30 years ago. Apparently Microsoft has no conference rooms (people have large enough hard-wall offices that they just meet in somebody's office) so the conference-room scheduling is only now (after 20 years) becoming usable.
The dark side of "progress" here in the 21st century.