From the instrument company they had a 4-channel RS-232 "Autoswitch" you could wire into the serial port from 4 instruments, then the fifth cable ran to a dumb terminal CRT console, and you could access any one of the instruments by sending unique control codes to switch communication channels.

Those Autoswitches were about a $1000 option. Instead, most people who were doing something like this used a manual switch from Radio Shack that was about 50 bucks.

Alternatively, you could unplug the local CRT terminal and connect the serial cable to a phone modem instead. Your instruments then had a telephone number.

You could then call from anywhere to access the data and control the instruments. As long as you had a modem and terminal at any remote location. Long-distance charges may apply :)

Using 1980's design equipment.

In 2001 the Sony smartphone made it possible to remotely call in on a cellular, link it to your laptop by infrared, and use Hyperterminal in Windows XP instead of a local CRT if you wanted to also. They had this to an extent before XP, Bluetooth, and USB anyway.

But with a manual switch you couldn't switch instruments remotely 24/7 unless there was somebody on site 24/7, not without an autoswitch.

At Exxon, 4 channels was not enough, and there were AT&T rack units like this, way more powerful, with built-in modems for direct connection to the phone lines.

Never did use the rack one I got since all my instruments were in the same lab at the time, and before I could make a move, ethernet became dominant which joined each instrument's PC quite well when it was built into Windows, instead of having to join instruments together in some way beforehand.

All I had to do so I could have a PC for each of the old RS-232 instruments was to "just" write my own code to accomplish both, "concurrently" for instruments never designed for DOS interfacing, much less Windows.

You could list your fax number if you wanted to but that was likely to get you more fax spam.

It was expected if you wanted people to have your fax number, you would do that the way you wanted to. Subway sandwiches always listed their fax number and put it in their ads, at noon there would be numerous people breezing through the line who had faxed in a Subway order form from the office. About the equivalent of ordering in advance from the app today.

I mainly faxed outgoing finished paperwork manually (that had been autoprinted by my 80's Exxon Intelligent Typewriters) or recieved confirmation of international orders that I already knew were coming [0] so when I got the internet I could basically tie up my fax line a lot without missing any incoming calls on the main number. When I was there after hours though, I could tie up both lines and I did that a lot to double my download speed. IIRC joining two modems in Windows became possible in W95 or W98 but I never actually did that.

Just used two PCs on two desks with one running the business ISP account and the other dialing-up to the home account.

Napstering in stereo screech :)

[0] My own company was the first marine place I worked where it didn't start out needing a Telex to serve as official cable confirmation of job orders. In the early 80's nobody had ever heard of fax machines because they were called telecopiers. Where you manually clamped a letter-size piece of thermal-sensitive paper onto a horizontal drum to receive a page. We had some of the better ones called Exxon Qyp where you talked to the other party using phones that were wired into the Qyp, then pushed the button to go into copier mode and it acted like an Edison phonograph cylinder where the sender ran its scanning head around the cylinder from top to bottom on their original document, simultaneously the reciever would run its thermal bit-printing head in the same pattern down their blank media page. As line speeds increased beyond 300bps, more modern machines became possible to send a page at a time, with digital memory no longer expensive as unobtainium, buffers came along. But it still wasn't good enough, you still needed a Telex until one day these documents finally became officially acceptable, as . . . wait for it . . . facsimilies.

That's exactly what it was.

According to monopoly regulation, the vast number of residential phone lines were intended to be subsidized by the lesser number of business lines from the beginning.