As noted in previous posts, N call signs are used both for aircraft and Amateur. There shouldn't be any duplication of those call signs, but there have been. There are instances of an Extra Class ham operator having the same N call sign as a plane. My guess is that either the FCC or the FAA goofed. One other interesting thing is that FAA Air Traffic Control doesn't use the N on the air when speaking to pilots. If they are in contact with a plane with the call N123AH, they will simply say "1-2-3 Alpha Hotel."