It's not completely clear how much thinner the iPhone 5 will be than the current iPhone. However, we've heard that the touch panel will be thinner, as will the screen, which is reportedly made of Corning's Gorilla Glass 2. Leaked images of a phone that looks thinner than the current model seems to bear out this rumor.
Probability: Count on it. All clues point to "yes."
(Image credit: chrisbrownie91 on YouTube.)