In the movie, at some point when Michael and Julianne are in her room (I think) and he rings Kimmy, his fiancee, he gets someone else on the end of the line, and asks to speak to Cameron. Kimmy was played by Cameron Diaz.
He doesn't ask for Cameron. He asks to speak to Kim. He was upset, so understandably he didn't think of her as his adorable little Kimmy at that point!
Snozberries is exactly right - I have this movie and watched this scene over and over, and he asks for KIM, not Cameron. Listen closely and you'll hear it too. =)