Oh how the tides have turned.

You could get ISDN2 installed on domestic premises in the UK. It wasn't cheap though, because as soon as you wanted a bonded 128k channel the cost could become somewhat eye watering for a domestic user (or even a small business).

The good thing though was that you got a guaranteed 64k rather than the vagueries of a 56k modem that in practice never actually worked at 56k, more like 30-45k depending on phone line quality.

On top of that you could (if your wallet was fat enough) get ISDN30 (E1) which was akin to a T1 but ~500k faster.

I did a fair amount of commissioning of these things back in the 90's.

Residential ISDN was very rare in the US. I rented a house in the 90s with a few fellow nerds and we got ISDN in our house, but it was definitely expensive (and required a network terminal device) and you always had to be routed to a specialist at the phone company if there were any issues, since most of the support people had never heard of it.