What? HD Voice using VoLTE or WiFi Calling is miles better than any land line phone

I'd take a landline over the inconsistency of cell calls any day. Maybe peak/maximum quality is better with today's tech, but reliability definitely isn't. I would bet average quality of calls has dropped too. HD voice is a carrier specific thing, no? Most of the time I can barely even hear the other person, much less have HD anything.

I think you have been misinformed. Voice calls over plain old telephone service were band-limited to <4khz decades before cell phones became popular. This was necessary in order to cram more active calls into our existing telephone infrastructure.

Digital phone calls today are way better.

Today's g.722 (HD Voice) is better, but GSM codecs are also 8kHz sampled, then lossily encoded. If the compression is appropriate, gsm is 13-bit per sample vs 8-bit per sample commonly used for POTS (minus robbed bit signalling in the US), but if the compression isn't appropriate, you get some pretty nasty artifacts. Encode/decode delay can be significant in some applications, but since GSM is TDMA anyway, you're going to have buffering and may as well use that to encode; a T1 PRI multiplexes one sample at a time, so a lot less delay there.

I’m sure that’s all true. I’m also pretty sure I wasn’t regularly shouting into my AT&T landline “I can’t hear you!” Obviously we’ve gained a lot with cell phones and portable music playing but it’s been mostly at the cost of consistent quality.