And I've worked on telemetry devices which had modem and could phone alarms and data to control room over landlines before there was any ISDN available. This wa

And I've worked on telemetry devices which had modem and could phone alarms and data to control room over landlines before there was any ISDN available. This was for city heating control. My company was upgrading this to mobile connectivity. Whole system earned it's worth after one pipe break, because operator could select area on map, turn off all flow to different devices with several clicks and they didn't have to use complicated freezing devices to fix pipe.