Character mistake: When Kyle steals the police officer's gun and asks him what the date is, the officer replies "12th, May, Thursday". The film is set in 1984. May 12th, 1984 was a Saturday.
Character mistake: When the Terminator walks into the gun store, the "Clearance" sign in the window is misspelled "Clearnce." (00:13:40)
Character mistake: In the final scene at the Mexican gas station there's a sign that says "cigaros" instead of "cigarros," which means "cigars" in Spanish.
Answer: Gonna be totally honest... that might just be nothing more than a simple continuity error. They accidentally made a phonebook prop that didn't match up with the locations where they shot, and assumed most people wouldn't notice or care. (And to be even more honest, I never noticed it until I saw this question today.)
TedStixon