ISDN was widely available in the US (it ran on the same copper pairs you already had) but was never all that popular. You could essentially _always_ get it deployed and it was the base-level connectivity back in the 90s for remote sites. I had it installed in a few crappy apartments much to the confusion of the local installers, the line price wasn't crazy expensive but finding a local ISP that would agree to reasonable always-on pricing was more challenging.