This was back in the days of 2400bps dial-up modems, and line noise on copper wires never intended for digital use was an ongoing problem, more for some users than others. A bit of static on the line would create a burst of gibberish in the chatroom.
On one occasion, a particularly weird bit of line noise generated a splat of random symbols that looked rather like a Lovecraftian invocation of the Great Old Ones -- "Ia! Ia! Fthagn!" etc. (It wasn't quite that exact.)
We had, in fact, been discussing Lovecraft at the time, and someone remarked on the line noise, calling it "Pickman's modem at work," riffing on Lovecraft's short story "Pickman's Model."
I don't remember who said that, alas; I'd like to give credit where it's due, but I can't. Whoever it was, I promptly asked if I could have the phrase as a title, and was given permission. I then wrote the story to accompany the title, and sent it to Gardner Dozois (who had been in the chat room when all this began), who bought it for Asimov's.
Not long thereafter the late James Turner, then editor at Arkham House, invited me to submit something to an anthology called Cthulhu 2000, and I sent him "Pickman's Modem," which he bought as a reprint. Gardner also reprinted it in an anthology called Isaac Asimov's SF-Lite. It's been around, for a story I wrote in a couple of hours on a whim -- it's even been translated into Italian. And I included it in my collection Celestial Debris.
Alas, the story is badly dated now -- the technology in it is hopelessly obsolete. I doubt most people nowadays even know what "line noise" is. Or rather, was. I think it amused readers in its day, though.
That's it; here's your list of handy exits: