Daring Fireball notes that in 2006, a year before the release of any iPhone, Apple had patented the use of ceramics as a encasement material for devices like iPods (they used a iPod Mini in the drawings). Perhaps this is the backing of that iPhoneHD we’ve been seeing.
The benefits: harder, more scratch resistant and radio transparent than aluminum, Apple’s current material of choice. While plastic is also radio transparent, Apple may be looking at harder materials.
Additionally, we, along with a few others, have been hearing that the back of the iPhone is going to be made of a glass-like substance and you might have a perfect storm of ceramics. That Engadget phone’s back looks awfully glassy.
Zirconia may be embodied in a variety of colors including white, black, navy blue, ivory, brown, dark blue, light blue, platinum, gold (among others).
Interestingly, Daring Fireball notes that having glass on one side of the iPhone gives you a 50% chance of losing it when dropping it. Having glass on the back would make losing it a forgone conclusion in this scenario.
Perhaps in a 2-D world, this would be the case. But, I’ve dropped my iPhone on its side on more than one occasion only to have it bounce away unscathed. Apple wraps the plastic around the side on its current models for this very reason. The new phones look to have aluminum on the sides which would also prevent a lot of breakage.