Greetings: hei, (heippa), moi, moikka, moro, terve, päivää, and we also use foreign hello and ciao, but we may write them helou and tsau as we say them.
When answering the phone you can use all those if you know the caller and it's an informal call. Otherwise you can answer by your name or just "haloo".
Bye byes: heippa, heipat, hei hei, moikka, se on moro, moi moi, palataan, nähdään and many many variations. And in formal situations just "hei" or "kiitos hei" or "hei hei, kiitos" if you want to add thanks. (If you want to sound like an old movie you can also use näkemiin or hyvästi.)