I think different countries have different norms around things like landlines - or even texting. In the US, people ignored texting for a very long time and preferred to call people even if it was just a short note.
In terms of audio quality, VoLTE has improved that quite a bit when both sides will inter-operate with HD voice. Older stuff often used 8-12kbps and primitive codecs to encode your voice which simply a lot of compression. I know Speex has had some great results at low bitrates, but that's a far newer codec. However, I believe VoLTE's AMR-WB codec still chops everything about 7,000 Hz. T-Mobile US and Verizon have both implemented EVS which goes up to 14,000 Hz.
https://www.pcmag.com/how-to/how-to-make-your-cell-phone-cal...
Of course I'd find a Sascha Segan article when looking to confirm some information. It has some great recordings to compare and you can see huge differences depending on carrier implementations. The Sprint-Sprint test shows very poor quality. The T-Mobile 2G test also shows how old networks just used poor codecs with limited bitrates. You can even hear distinct differences between the T-Mobile-T-Mobile call and the Verizon-Verizon call where the Verizon call just sounds significantly less rich.
Back in the day, calls used a huge amount of network capacity. Even today, because calls need a more guaranteed bitrate, networks need to leave some extra room for them. 128kbps of streaming music isn't the same as 128kbps of real-time voice because the network can deliver 15 seconds of music and then it can deliver the 16th second of music any time in the next 15 seconds. Real-time two-way communications don't have that luxury. Still, bumping up the bitrate on communications makes a big difference and networks today should be more than capable of handling it.
I don't know what German operators have implemented, but cell phones have come a decent way in terms of audio quality, though carriers being lazy and interoperability problems can mean that consumers don't always get the benefits in the real world.