Forgive me Lanren but we talk how to do just back curvy part of the phone
I think you should take a look in depth at examples Michael and Adamio previously highlighted you :

go directely to the middle of the post here: http://moi3d.com/forum/index.php?webtag=MOI&msg=3137.1

here shows different Rhino's method: http://cadjunkie.com/1515/the-dreaded-3-way-corner