Do You Remember ISDN? (youtube.com)

I remember. It was very expensive for not a lot of extra bandwidth. You also needed a special ISDN phone or a, again expensive, box to convert the signal to normal POTS.

Not long after the cable company started offering 'broadband' at 115 kbps, quickly upgraded to 512kbps.

ISDN was a complete non-starter in my locale.

Had ISDN in the mid-90s back when I worked for an ISP. Wasn't expensive from my telco, 40 1996 dollars a month and the cost of a Motorola BitSURFR Pro. Got dial-up bonding working on the ISP side. It could "ring through" one of the B-channels when a call came in and stay connected on the other. A wonderful time.

I remember FSOL ISDN https://www.youtube.com/watch?v=VAuMvNt4dr0

(https://en.wikipedia.org/wiki/ISDN_(album))

Sure. The first internet connection where I worked in the 1990s was ISDN with (I think) an Ascend P50 router. Don't remember what it cost. We used the ISDN strictly for data, not also voice, which was still provided over POTS lines.

Was next upgraded to a VDSL connection that ran at T1 speed, 1.544 Mbps.

Oh yeah, we had it in our house because my gf at the time was a tech for an ISP. IIRC, that was the first "broadband" we had, and was replaced by DSL shortly thereafter.