The "best" nostalgic connection would be mid 1990s to whenever 2000s ISDN where you have end to end PCM on a nailed down circuit switched network.
There are a lot of issues to deal with going 2 wire to 4 wire to some kind of carrier and back again in an all analog network, and once you introduce some kind of hybrid network like PCM carrier and TDM switching any remaining analog links are only a liability.
Modern codecs can pack a lot more quality into less bits and with FEC.. so an HD Voice VoLTE or Opus VoIP call are technically "better" than anything used for baseband voice on circuit switched networks in the past. You could easily recreate circuits with dedicated fiber wavelengths these days and have the best of all worlds.
There are a lot of issues to deal with going 2 wire to 4 wire to some kind of carrier and back again in an all analog network, and once you introduce some kind of hybrid network like PCM carrier and TDM switching any remaining analog links are only a liability.
Modern codecs can pack a lot more quality into less bits and with FEC.. so an HD Voice VoLTE or Opus VoIP call are technically "better" than anything used for baseband voice on circuit switched networks in the past. You could easily recreate circuits with dedicated fiber wavelengths these days and have the best of all worlds.