My first modem was an AT&T 300 baud acoustic coupler. My last was a USRobotics 56k for the BBS I ran till the early 2000s.

I later switched to DSL for my Internet, but the reason we never did this sort of thing was the ISDN was just easier to get bandwidth and the tech existed to do what you needed with a few of them.

12x POTS lines, or 6 full duplex ISDNs.

My 56k never actually achieved that, most of the time it was 33.6 or 28.8.

This is neat, and fun to see them still being tinkered with.