why on tv or movies does a phone number always start with 555?

"The phone companies began encouraging the producers of television shows and movies to use the 555 prefix for fictional telephone numbers, roughly during the 1960s. One of the earliest uses of a 555 number can be seen in Panic in Year Zero! (1962), with 555-2106. In older television shows from the 1950s or 1960s, "KLondike 5" or "KLamath 5" was used, as at the time the telephone exchanges used letters and numbers in phone numbers. More recent works set in this period typically use this convention as well. For example, Dr. Emmett Brown's 1955 phone number in Back to the Future is "KLondike 5-4385". The 1985 Jennifer Parker character writes the number 555-4823 on the clock tower flier telling Marty to call her at her grandmother's."

http://en.wikipedia.org/wiki/555_%28telephone_numb...

You are right. :) There was an article about this in a recent mental_floss magazine, but I can't find the issue. I already knew about the number being used in movies, etc. but I didn't know the history behind it until I read this article. They did it because they found that Americans like to call numbers that they hear on TV or the radio. (Have you heard the song "867-5309"? That person had to change their number and I guess it is now no longer used.) The numbers 555-0100 through 555-0199 are designated for this purpose. Wikipedia has a page on it, but it is pretty sloppy (needs editing). Wish I could find that magazine!!