This is a weird article that imagines that businesses skipped straight from analog -> IP. They mostly didn’t. Mid-size and larger businesses had been running digital phones and PBX systems for years and years prior to IP phones.
But on the small business end, most businesses are doing just that right now... Going from one or two analog lines to a cloud managed IP solution.
We had Merlins at my parents' store when I was growing up, and an interesting artifact of the analog channel was that some analog data was possible. For instance, we hung a fax off one of the Merlins (14.4k was fine); I likewise got get 33.6k off it when I plugged in my modem, but could never get 56k. In hindsight, that's because 56k actually requires the line to support digital signalling, which the Merlin did not.