Don't forget video games.

In a game with good network code such as Quake 2 / 3, you could expect at best a 150ms ping time with a 56k modem in ideal scenarios but on ISDN you could get half that which made a world of a difference.

I never had ISDN but I knew a few people with it. It was like you were playing a completely different game. Then cable came and it blew everything away with getting 20-30ms ping times even in the early 2000s.