One Missed Call?[spoiler]

Seen the movie? Ha, want to explain it to me?
[spoiler if you haven't seen it]

So, I get that the girl [ellie] was hurting her little sister [laura] and her mom found out and then locked her in the room-she had an asthma attack and her inhaler wasn't working, and the bear with the camera and yeah you get what I mean right?

-Why was Ellie hurting her?
-Who was the first to die?
-Who was this Ellie trying to call?
-And how does this have anyhting to do with the main character [Beth]'s past?!

and why does the cool detective dude have to die!!!!!!

v__v

So confused.

But I loved the movie (:

Help?