Were not sure when the iPhone 5 will be in consumers" hands; the last bit of iPhone-related development news suggested a minor update this year with refreshed hardware specifications, but keeping the same overall design. If the release of the iPhone 5 happens sometime in the near future, but not this year, then they might go for a new design refresh. The older iPhones prior to the fourth generation had curved backs, with a rather boxy design for the iPhone 4. The iPhone 5 may just have curves all around, including the screen itself, according to the latest bit out of the rumour mill.
According to DigiTimes, there are rumours out of the Taiwanese supply chain of Apples push towards a curved glass design for the iPhone 5, much like the fourth and fifth generation iPod nanos as depicted above. Apple has reportedly purchased about 200 to 300 glass cutting machines in response to the reluctance by cover glass makers to commit significant investment into glass cutting machines given the high capital involved. Apples machines wont be used and will be kept in storage until there is a greater yield of curved glass screens.
In either case, if this rumour rings true, then it can be safe to say that we still have quite a bit of time before we have leaked iPhone 5 prototypes being spotted in the wild.
Image Credit: Dietary Health Blog @ Yovia