ISDN did have multiple channels, in Germany you would get two data channels (B1 and B2-channel, 64 kB/s), and the line has a D-channel (something like 4kB/s) for network purposes. First you could bundle the B-channels to get twice the speed, at twice the price and the land line was busy if one did that. That feature got me into trouble with my parents quite regularly.
Second someone figured out that the D-channel can also be used to send data to arbitrary endpoints in the phone networks and dropped a messenger app on a Friday afternoon in '98 or thereabout. That was a pretty fun weekend, unfortunately the hack had stopped working when I came back from school on Monday.
Second someone figured out that the D-channel can also be used to send data to arbitrary endpoints in the phone networks and dropped a messenger app on a Friday afternoon in '98 or thereabout. That was a pretty fun weekend, unfortunately the hack had stopped working when I came back from school on Monday.