The very first OB I did for the radio station was for the launch of the National Lottery. Bearing in mind I'd been in the job about six weeks at this point, I was slightly amused to turn up on site to see the head and shoulders of a BT engineer emerge from a manhole and proffer me a (slightly) twisted pair with the ends bared.
"There's your line".
Of course, this was before digital lines, ISDN etc. It was (IIRC) something called an "EPS85", which was an 8kHz analogue line back to the exchange, where another engineer jumpered it to the line going to our studio. This was also in the days when we had the phone numbers for the exchange racks rooms and could call the phone nearest the place where our lines terminated to get the attention of the on-site engineer.
Screwed the pair into our "connect anything to anything" box, plugged that into the mixer, and within a few minutes we were on air. Simpler times.
Helped the local station do an OB from the museum I now work at a few months ago. They were panicing because they couldn't get a good enough WiFi connection for their email to work on one laptop, and the other laptop - which was supposed to be able to remote-control the playout system - wouldn't see the network at all. So many people in the area that 3G and 4G were out of the question. Fortunately they were doing audio via ISDN.
Them upstairs keep trying to take my ISDN off me, but they can pry it from my cold dead hands :-)