Re: Emergeny calls
You could even get DC connected leased lines at one time - ie. a direct physical pair of cables from one side of town to another.
A blessing and a curse. Working for ILR we had several of those things - EPS85 (IIRC) to the sports grounds, for example. Problem was that a typical BT engineer, rocking up at a local DP looking for a spare pair for a temporary phone line would put his meter across the pairs in turn and finding neither 50V or 75V (POTS or ISDN) assume the line was free. We would often find our lines suddenly stopped working just before (say) a major international rugby match.
We fed programme constantly up the line, and when the OB kit was unplugged at the stadium it was looped back to our racks, so the procedure - in the days leading up to a match - was to check for programme on each line, probably daily and certainly both the day before and on the morning of the match. No programme? Instant callout. Or in the case of the National Stadium, a quick jog up the road, probably get there before the engineer has finished and point out what he's done...
I've recounted here previously that a week or three after starting work at the radio station - my first "proper" job out of university and still very much finding my feet - we did an OB for the breakfast show. Most of the stuff could not be set up until the morning, so I turned up very early with cables and connectors, wondering where our temporary line would terminate, to be surprised when an engineer poked his head out of a hole in the road and handed me a scraggy bit of telephone cable with one pair twisted out. "There you go".
8½kHz back to the studio. It "just worked".
Of course, it wasn't long before ISDN became more convenient and then - eventually - the problems with IP were mostly sorted, though for OBs which may not have a thoroughly robust network connection, dropped packets and latency can still be issues.
Our FM signal used starquad to the local transmitter with an amplifier at the exchange. The more distant transmitter used starquad to the exchange and then NICAM to the transmitter. Both our AM feeds used EPS85 (or something similar, can't really remember the designations now) on bog standard twisted pair, bundled in with all the phone lines. We had a memorable occasion where a pair of likely lads was replacing a bit of cable outside our studio, listening to the AM service on their radio, and one of them - when we went off air - jokingly said to the other "did you just cut the wrong pair?"
Yup, of course he had...