From my user's perspective, it seems that privatization of Germany's phone and Internet market has worked pretty well, and lowered prices all around.
Though I don't know if that was because there was a huge boom of Internet access around that time, and telephony prices would have dropped anyway, or if that was one of the examples where it did work, inherently.
Because your telecom regulator has teeth and there's competition? When German T-Com bought Slovak Telecom monopoly they continued just like that. Forced old ISDN tech on everyone for high prices (probably to clear out stockpiles) and suppressed DSL for a few years, till some last mile access for competition was required by law.
BTW was in Germany myself many times and it's surprising how bad coverage there's outside city centers.
LTE/5G data is extremely expensive in Germany compared to essentially everywhere else in the EU.
Here’sa comparison what 30 EUR per month for you in terms of LTE data volume in 2016, and I don’t think there’s any real contracts with unlimited volume available for 30 EUR still: https://imgur.com/NXu0ZoP
Getting a contract for unlimited data with the German Telekom costs 85 EUR/mo currently, while it would cost 35 EUR on t-mobile.nl
Funnily enough, in my experience Germany has the same (actually seemingly worse) issue as the UK; many people have poor home internet speeds due to the fact that the local (copper?) legacy infrastructure is privately owned by DT/BT, and there is little to no incentive to have that upgraded
Though I don't know if that was because there was a huge boom of Internet access around that time, and telephony prices would have dropped anyway, or if that was one of the examples where it did work, inherently.