As I've mentioned before, Japanese has a lot of set phrases that are very handy as they're used all the time in certain situations.
One of them is "moshi moshi". I've noticed more and more Americans seem to know this word, but they're unaware of when it's actually used. "Moshi moshi" means "hello," but is only used on the telephone. It is never used to greet someone standing in front of you.
The history of this phrase is rather cool: way back when people used to say "moshi" (from "mousu" 申す, "to speak") to call out to someone and start a conversation. However, they would say it twice to prove they were living, warm-blooded people who weren't ghosts or ghouls.
Ghosts can't repeat the sound "moshi". So if you heard a single "moshi" coming from behind you, it was best to not turn around. If you turned and answered, the ghost would steal your soul.
With the invention of the telephone, this tradition carried over to it (if you think about it, being on the phone is like having your back turned in that you can't see the person).