Update, 12/23/14: More documentation has been found! Matt Novak, at Gizmodo's Paleofuture blog, has found evidence that the NORAD story, as repeated below and as Snopes has it, is partially true but partially the stuff of myth—and, in both capacities, the stuff of savvy military PR. According to Novak, "Yes, Colonel Shoup got a call at CONAD that turned out to be a wrong number. But it wasn't on Christmas Eve and there was no misprint in the newspaper, even though Snopes claims there was. It was just some kid who happened to get his numbers mixed up. And as for Colonel Shoup's reaction? It was more like the kind of reaction you'd expect from a military officer in charge of ordering a strike that had the potential to end life on Earth as we know it. Which is to say, Shoup was not amused. And he wasn't inundated with calls throughout the night that his men had to take."

More here, and big thanks (again!) to Yoni Appelbaum for pointing out the new information.

It was 1955, and Christmas was approaching, and Sears had a new idea for a yuletide gimmick. In local newspapers, the department store placed ads ... on behalf of Santa himself.

"HEY, KIDDIES!" the ad read, in a greeting that would seem creepy only in retrospect. "Call me on my private phone and I will talk to you personally any time day or night."

The ads then listed local numbers for area children to call to get some one-on-one Kringle time. Which must have seemed, if you were a kid back then, pretty amazing. A direct line to St. Nick! Kids could, finally, bypass the middlemen that stood between them and their gifts—the Post Office, their parents—and go directly to the source. And, even more directly, to that source's enormous bag of loot. You can almost hear the Ralphie Parker voice-over.

Like many innovations, though, Sears's frictionless Santa scheme found itself with an unforeseen problem. In the ad the company had placed in the local paper in Colorado Springs, Colorado, Sears had listed Santa's number as ME 2-6681. Which, according to Snopes, contained a typo: It was one digit off of the intended one. The number Sears had ended up printing and distributing to the city's citizens? The one for, as it happened, the Continental Air Defense Command (CONAD)—the predecessor of NORAD—which, like Santa, specialized in aeronautics. And which, unlike Santa, was based in Colorado Springs.

Suddenly, on Christmas Eve, phone calls intended for St. Nick were being received on a top-secret NORAD line—a line that was usually reserved for crises (which, back then, pretty much meant "Russians attacking"). When the first call came in, Colonel Harry Shoup, the officer on duty at CONAD, picked up the phone.

"Yes, Sir, this is Colonel Shoup."

As Mentalfloss puts it, the colonel received no reply—just silence.

“Sir? This is Colonel Shoup,” he said again.