There are band filters and such on legacy, fully analog systems. G.711 (which is standard now for non-cellular call audio) is a step down, but Opus at 16Kbps s

There are band filters and such on legacy, fully analog systems. G.711 (which is standard now for non-cellular call audio) is a step down, but Opus at 16Kbps sounds better to me than a classic, full analog system due to the lack of band cutoff & smarter encoding.