여보세요 means literally "look here' = 여기 보세요. It is used when answering the phone. In this situation it means simply "hello". It is just an idiomatic expression 여보 is used among older married couples to call each other. Young people tend to use 자기야 instead.

As 프란시스코 said, 여보 is 여기 + 보오. 여보세요 is the same, too. 세요 is like a honorific ending. e.g. 벌써 가? 벌써 가세요?, 어서 해. 어서 하세요. The latter is more polite.

yeoboseyo and yeobo literally means peace (not quite sure) but those words are often use as hello just like anyeonghaseyo ..by the way i think we can help each other in learning korean i can read hangeul but not that good and can understand some words so..Let's be friends