It's amazing to remember how crystal clear phone calls used to be. I wonder if there's a niche for the first service willing to use more bytes and sacrifice efficiency in the name of analog-era call quality.
What you are calling "analog-era call quality" was likely mostly digital call quality, with only the local loop being analog. Before digital carrier facilities and switches like 4ESS, 5ESS, etc. became ubiquitous on the PSTN, there was plenty of analog noise on local and long distance calls, as well as delays, echo, crosstalk, and other artifacts. I remember a marked improvement in voice call quality throughout the 1980's. I believe wireless voice quality will increase organically as the bandwidth available for wireless digital services grows.
But telephony has always been band-limited to 3 kHz, even in the 'good old days' of analog lines. Voice quality over a transatlantic link compounded that with delays, static and fading. If you needed high quality audio over the phone system, it _was_ possible to book a 'music line' for things like outside broadcasts that did not have the aggressive filtering, though.
T-Mobile is what I have. I think they were the first?
But it sounds great on T-Mobile. I usually just talk to the wife both of us on iPhones and T-Mobile. And then I get the occasional call from someone else and I am like "What the !@# get a decent connection/phone/whatever!"
Frankly I doubt it. With Facebook, Skype, whatsapp etc all offering free, high quality calling, it's more likely for it to fade away than be replaced by a higher quality product.