[0]: https://www.revk.uk/2017/12/its-official-adsl-works-over-wet...
But it sure is nice to be able to make phone calls where people don't sound worse than they did with digitally-switched analog landline telephones in 1995. Bluetooth doesn't get there at all.
The losses of Bluetooth even compound generationally: The inescapable tin-can audio of Bluetooth at one end first gets transmogrified by at least one intermediate lossy codec for transmission across/betwixt the network(s), and then gets tin-canned harder when the far end of the connection is also using Bluetooth.
For perspective: 1995's phone calls were ultimately limited by the G.711 codec, which itself dates to 1972. I'm not setting the bar very high here at all.
Of course that sounds like a tin can either way, it's coming in encoded with the quality of a tin can! People here are talking about modern VoIP calls (Teams/Slack/Discord/Zoom/etc) which have a snowball's chance in hell of sounding decent in the first place. HSP/HFP will often crank that right back down to traditional phone network quality again. You also lose stereo, which isn't so bad if the only thing you're doing is having a 1:1 call but kind of sucks for a background group call.
But now that you mention it: Yeah, the state of common VoIP (Teams/Slack/Zoom/whatever) is also usually not very good. It's like there's some huge bandwidth crunch here in 2026 that is driven by the strenuous demands of VoIP, except: There isn't.
When I was doing some live streaming with others in a studio a couple of years ago, we worked with some of that. It never sounded very good. (It doesn't sound very good when the big-time acts at CBS or NPR or Fox News do it, either.)
But! When we occasionally had remote co-hosts who had enough technical competence to make it work properly on their end, we were able to use SonoBus[1]. That audio was positively pristine, like they were sitting unseen in the same room as everyone else.