Well, I've been watching American TV since Alias Smith & Jones and Kojak in the early 70s, and I can assure you that in all that time I never ever knew that 555 was a fictional phone exchange! (Happy Days, Cagney & Lacey, Murder She Wrote, The Rockford Files, Friends, Taxi, Cheers, Frasier... and all the Star Treks - oh wait... )