VoIP is Still a Thing
I don't write much about VoIP anymore. Of course, I don't write about much. Maybe if I string enough of my WhatsApp/SMS/iMessages together, I could write a book. In fact, I bet we all could :)
That said, VoIP is still a thing. Businesses are still looking for a way to lower costs and make it easier to connect their employees. What's surprising to me, at least, is that one name is still there from back when I was writing about VoIP on a regular basis: 8x8! The others are fairly new, though Ooma and Ring Central have "sponsored" radio-related things I've listened to recently.
Me, personally? The only VoIP app I use with any regularity is WhatsApp. Not sure how Facebook makes money off it. But clearly, the solutions below are making some money. And if you're in the market, they're worth a look.