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When I was in college in the '80s, My roommate and I got curious about unused area codes (and/or prefixes? I forget). We started dialing some. Within about 15 minutes we stumbled on some government service with a scary-official sounding operator on the other end (I've no idea if it was this service or a different one).

The really scary part was after dialing the number and encountering the operator, we were unable to hang up (any time we hung up and picked back up, the operator was still there, even after waiting about two minutes). Fortunately this was (a) at MIT which still had a central electromechanical telephone switch for student phone lines in the '80s and (b) I had keys to the switch as a student phone repair tech.

I still remember grabbing my keys, running over to the switch, and physically pulling the relay contacts to release the call and prevent a trace to our location in case that was the motivation for holding the line (nowadays traces are digital and instantaneous, but when looking at old-school electromechanical switches you really did need time to trace the call physically through the relays).

Yes, we were aware the operator was probably just messing with us by showing he could hold our line against our will to discourage us from calling again, but it still scared the crap out of us just in case.

Very interesting story, curious if you remember the number. Reminded me of my favorite scene from Community: https://youtu.be/xx_MkKJPNjQ

My recollection is we were specifically curious about what today would be called invalid address space patterns, aka numbers that were outside the patterns used in valid phone numbers at the time (such as area codes could have a 1 in the middle digit but prefixes could not have a 1 in the middle in the 1980's).

We pulled out a paper phone book, devised a set of criteria for potentially interesting superficially invalid phone numbers, and started dialing them. On a rotary dial phone. And we found one pretty quickly. And it was a much scarier experience than we had expected.

The exact number we dialed is unfortunately(?) lost to the passage of time.

Here's a fun one: next time you get a new phone number (USA), ask for it to end in "9999". It's possible, but not without social engineering (or influence?).

When I last got a new cell number I got one ending in "5555" Annoyingly I use Google Voice so something like 6 people actually know my awesome number.

you can port out your number to google voice....

Telco used to charge extra for vanity numbers. c2000 I paid Qwest a few hundred for one.

Why is it restricted (and who to)?

Let's find out

Find out! :)

How is hanging up (creating an open circuit) different than pulling the relay (creating an open circuit)?

The phone circuit in the analog days was physical. It doesn't matter that it was open, the relays between one and and another were all connected and could be inspected.

It's analogous to finding the hardware corresponding to someone's network address by being able to inspect the routing tables of all the intervening routers. Even if they turn their computer off, you can still trace them back to the physical line.

IIRC you could send power to the relays from the calling side, which'd keep them latched even if the callee hangs up.

Even if the circuit is still open from the telco trunk to the dormitory switch, the link back to the specific extension that dialed out would be broken.

Sounds like someone had god mode

Maybe not so nefarious. Back in the 1980s the campus phone system at my university had a similar quirk: if you didn't hang up both ends of the call, the connection stayed open. A common DOS prank was to call someone and then just not hang up. Their phone was then unusable.

Ah yes. The old Dormphone system that was regularly hacked/extended in various ways and reverted in a pretty much never ending tug of war.

What was the conversation like? Was the operator trying to scare you off?

I had a friend in HS do this to me, I always attributed it to his father being pretty high up at a local newspaper ... ( The Netherlands )

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