At the end of the century, 1999, I had one of the first and also one of the last ISDN internet flatrates, offered here in Germany. It cost around 60 Deutsche Mark per month. Around year 2000 this ISDN flatrate became obsolete, because DSL was pushed into the market, also with a flatrate option. Now you could get 786kbit/s instead of 64kbit/s. :) I used my (and my only one) ISDN telephone to 2017 though. It lasted almost 20 years without any problems. Then we moved and now it is all VoIP.
We are still using our ISDN phone behind a FritzBox DSL Router. S0 Bus still works nicely and is much easier to setup compared to multiple VoIP phones in your house. Particularly supporting multiple phone numbers is nice. Actually all our phones we use are pre 2000s. The newer ones we had never lasted both in terms of design and tech. I think at work our Alcatel phone system also uses a modified version of the s0 bus (with numbers tied to the port )
ISDN was the gold standard after the 56k modem time. Low latency included, which was very nice for online gaming. It lasted for a while but then DSL came around the corner and it was game over for ISDN.
I must have had the same flatrate provider: Sonnet, I believe it was named.
It had perfect timing: starting in the market when I was fresh out of school and doing civil service as conscious objector, meaning I had a little bit of money to splurge for an ISDN flatrate at my parents house and it cancelled its ISDN flatrate tariff in fall 2000, when I moved out into my own little apartment and got T-DSL.
