• An aluminum border going completely around the outside
• Slightly smaller screen than the 3GS (but seemingly higher resolution)
• Everything is more squared off
• 3 grams heavier
• 16% Larger battery
• Internals components are shrunken, miniaturized and reduced to make room for the larger battery
Apple-connected John Gruber—from Daring Fireball—says that Apple has indeed lost a prototype iPhone and they want it back:
So I called around, and I now believe this is an actual unit from Apple — a unit Apple is very interested in getting back.
While we couldn't get it past the connect to iTunes screen for the reasons listed earlier, the USB cable on that screen was so high quality that it was impossible to discern individual pixels. We can't tell you the exact resolution of this next-generation iPhone, but it's much higher than the current iPhone 3GS.
According to the person who found it, this iPhone was running iPhone OS 4.0 before the iPhone 4.0 announcement. The person was able to play with it and see the iPhone 4.0 features. Then, Apple remotely killed the phone before we got access to it. We were unable to restore because each firmware is device specific—3GS firmware only loads on 3GS devices—and the there are no firmwares available for this unreleased phone. Which is another clue to its authenticity.