I sure a lot of people still do, why change, especially smaller companies that have no desire to change circuits and phones.
Probably no one is using Basic Rate Interface (BRI) circuits, they are using Primary Rate Interface (PRI) ISDN circuits, I supported and installed hundreds both of them at a Cisco TAC and for a couple of major companies.
I don’t know voice. I work on the data end of things, and there are so many solutions for moving more data faster and cheaper, that I assumed that ISDN went out the way 300 baud Hayes modems went out (faster modems using POTS are still in use at remote ATMs, POS, etc.).
Shows how little I know about a big topic.