I can't remember a book title!

I read a book a while ago about a girl who can hear a boy in her head. I wanted to read the sequel and I was waiting for it to me out, but I forgot what the first book was called! The voice in her head turns out to be a real person who meets her when he moves to her school. They meet in an elevator, and they don't like each other at first, but they end up falling in love. Does anyone know what it is?

-Erika