You don't say that, you either say "over" (I've finished talking, go ahead and talk more yourself) or you say "out" (I'm done talking on the radio now, bye).
I can only guess it was from Hollywood, but in the military no one uses it because it's wrong. People down vote for several reasons, but I don't worry about that usually, I'm just here to talk to others a bit and read about technology.
> Contrary to popular belief, "OVER" and "OUT" are never used at the same time, since their meanings are mutually exclusive.
I guess the question here is why is it a popcultural phrase?