"Guess what" and "You know what"

Question

I heard the phrases "Guess what" and "You know what" from movies and native speakers a lot, but I do not really catch the meaning implied.

1) Are they equal?

2) In what contexts one uses these phrases?

Answer 1

"Guess what?" Is usually used when you want to start a conversation on a new and interesting topic. Usually, this will be something that you think will surprise the listener or is something exciting that the listener will be happy to hear.

Guess what? I finally got that job I interviewed for!
Guess what? Jessica and Tim got married! Can you believe it?

"You know what?" Is generally used during conversation when you want to change the direction or topic of discussion. It is usually said abruptly and followed by a statement with a tone of finality.

You know what? All this sad talk is making me want to cry. Let's talk about something else.
You know what? I just realized that Jane was lying to me the whole time. She can be really selfish sometimes.

Answer 2

Colloquially, they both mean the same i.e. the listener is unaware of the fact that happened and that the fact may be surprising.

See this-

Yesterday, there was a match between Ricky and Mike. And guess what/you know what, Ricky won the match.

This means to the speaker and the listener, winning of Ricky is a bit surprising. Mike was expected to win the match. There, both the phrases can be used.

However, to me, guess what is a bit more surprising as we are telling someone the fact that the s/he had to guess it more than just know it.

Accidentally, he fell into the cage of the tiger and guess what, he came out alive after 20 minutes.

Using you know what here may surprise the listener but putting guess what denotes that the speaker certainly assumed that the fact is more fascinating.