"The program began on December 24, 1955 when a Sears department store placed an advertisement in a Colorado Springs newspaper which told children that they could telephone Santa Claus and included a number for them to call. However, the telephone number printed was incorrect and calls instead came through to Colorado Springs' Continental Air Defense Command (CONAD) Center. Colonel Shoup, who was on duty that night, told his staff to give all children that called in a "current location" for Santa Claus. A tradition began which continued when the North American Aerospace Defense Command (NORAD) replaced CONAD in 1958."

http://en.wikipedia.org/wiki/NORAD_Tracks_Santa