It turns out the NORAD tradition of tracking Santa Claus's sleigh as it nears U.S. airspace began as a wrong number.
In 1955, a special red phone sat on the desk of Colonel Harry Shoup of the Continental Air Defense Command. It was a hotline direct from the Pentagon, alerting CADC of an attack on the nation. As the NPR story notes, in December of 1955 Sears put an ad for kids to call Santa and gave his phone number, but the ad misprinted the number and gave a different one than Sears had set up -- one which turned out to be the secret hotline on Shoup's desk.
The colonel didn't realize this until children started calling the line, looking to speak with Santa. He figured it out and detailed some airmen to answer the calls, probably figuring that was the end of it until his Christmas Eve shift came and he saw some of those same airmen had made a mockup silhouette of a sleigh and reindeer for the big tracking board CADC used. He continued to play along and called local radio stations to report an unidentified flying object that looked like a sleigh.
Eventually the story came out about how CADC -- later the North American Aerospace Defense Command or NORAD -- had taken on the task of tracking the right jolly old elf and people wrote thank-you letters to Col. Shoup. His children say he carried those in a locked briefcase with the same watchfulness he would have given to the top-secret information he handled while serving at CADC.
One wonders if Soviet agents tried to use the suddenly well-known secret telephone number in some espionage scheme. It might not have worked, but they would have been winners either way -- those lumps of coal would come in mighty handy during exile in Siberia.