Before the advent of the telephone the word "hello" or "hullo" was not a greeting, but an exclamation of mild surprise, as in "hello, what's this?" I think it's in Alexander Graham Bell's patent application that he suggests that the greeting when answering a telephone should be "ahoy hoy". This is why The Simpsons' Mr Burns answers the phone that way, they're insinuating that he's old enough to have been told that's the way to do it.