> That is actually completely false.
There is certainly a lot more nuance to reality than my blanket statement was meant to imply but I assumed that went without saying. But I believe the underlying gist is accurate. Fancy encoding techniques got us quite far on analog phone lines, but my point was that attempting to transmit digital information over a highly-compressed audio stream optimized within an inch of its life for a small subset of human vocal sounds is going to be MUCH slower than over the analog phone lines of yesteryear. And at the end of the day, there is no substitute for bandwidth. Take it up with Claude Shannon if you like.
> I am not sure where do you live and what kind landline phones you had but modern digital cell phone codecs are light years ahead of the sound quality we had on land lines in 80s, esp. when calling long distance.
I lived in the Midwest US (and then later the West, with frequent calls across the country) and I quite distinctly remember the audio quality of POTS being quite good overall. Of course, not EVERY call was great. Some exchanges were noisy, some people's local loop or wiring in their house had issues, and some phones themselves were just garbage. But it mostly sounded great.
I'll grant that cell phone audio is more tolerable now than it WAS but it certainly was so bad for a while that from the early 2000's to the early 2010's, I pretty much only used cell phones for emergencies and actively avoided calling people on their cell phones if I could. The resulting audio was so distorted and muddy that I often could not understand the person on the other end. If it was someone I knew, I could often infer what they were saying from their speech patterns. But if it was someone I didn't know, or if they had a thick accent, there was always a lot of, "Can you repeat that again, more slowly this time?". I only cancelled my analog phone line after POTS network providers started switching their internal systems to VoIP (or something like it), bringing along all the same disadvantages of the bandwidth-constrained cell network.
Latency was also terrible, and continues to be. The analog POTS circuit-switched network was (modulo an audio buffer or two) speed of light. Modern digital voice communications buffer like crazy and up to two seconds of latency is extremely common. Maybe I'm an outlier as most people don't seem to notice but for some reason, even a half-second of latency is enough to make a conversation extremely awkward for me.