Worked at a hotel. Our phone system required you to dial 9 to reach an outside line on every phone except one: the fax machine, which was set up to dial that 9 automatically when you started dialing.

It would take a second to start making dialing sounds while it dialed that 9 in silence. Our AGM would dial the 1 before the area code, not hear any immediate sounds, and then press the 1 again. Then dial the rest of the number.

So as far as the switchboard I used to direct calls was concerned, someone just dialed 911. So it made the "holy fuck someone's dying" alarm, our local 911 dispatcher got to hear a fax machine screeching its handshake tones, and I got to go into "oh shit a guest is having a stroke" mode, only to find out that no, my manager didn't read the sign posted over the fax machine because of this behavior. Again.

And then we would get a call from 911 asking what the emergency was and have to explain that it was dialed by mistake.

Of course, this was almost always during a rush.

Great thing about fax machines. They can be set up in such a way that if they don't get a fax handshake, they wait a few minutes and try dialing the number again.