To say "hello" as in "good day" one may say 「こんにちは」[kon-nichi-wa] roughly translated as "As for today ... [it is good]." To say "hello? anybody there?" on the phone, one may say 「もしもし」 [moshi-moshi] or [moh-sh moh-sh] dropping off the final "i" on "shi" as often happens in spoken Japanese. There is the extremely colloquial and casual 「うっす」 (like "uss" in "puss") and is considered a lazy and cool way to greet very close friends but ought be avoided for use with elders and superiors. There is also the cheery and distance-shout 「ヤッホー」[yah-hoh!] similar to how Mario shouts on his triple jump in Super Mario 64. "Yah-hoh!" is quite casual and usually only used with friends, youngsters, and people one is very close to that do not fall into a respectful category of social interaction in the Politeness Hierarchy.