When on a call, what does the "flash" button do?

Hilarious thread and only reinforces what I've been saying in a lot of threads. Those of us "old far*s" (and I'm one of them at 59, soon to be 60) take for granted that so many of the younger generation knows a lot about this stuff. The truth is, they're often not only unfamiliar with it, but were never even EXPOSED to the things we grew up with. i remember the first days of being able to "flash" to another call..first, it was UNREAL that you could even GET a call coming in while you were on another call, but the whole flashing thing took a bit of practice. Do it too fast and you were not connected to the incoming call, do it too slowly and you hung up on the first call, lol. Remember the days when you could go to any pay phone and "flash out" the phone number you wanted to call without having to put a nickel (yep) or a dime in the slot?

Back in about 1960, me and my good buddy, who lived a few blocks away, set up a tin can with string thing. It was a very long distance to keep the proper tension on the string so it worked right, but we managed to make it happen. Then, another friend who lived in a house about halfway between us, wanted in on the action, so we tried making a T to loop him in. I seem to recall it worked...BARELY, but even the mere muffled sound of a voice, regardless of whether or not you could understand it, was a thrill!