The new iPhone will indeed be longer and thinner than the iPhone 4 and 4S. Approximate measurements are 125mm by 58.5mm by 7.4mm-a 10mm jump in height, nearly 2mm reduction in thickness, and virtually identical width. According to our source, Apple will make one major change to the rear casing, adding a metal panel to the central back of the new iPhone. This panel will be flat, not curved, and metal, not ceramic. Our artist's rendition provides a rough idea of what this change will look like; it echoes the current-generation iMac design, to be sure.
iLounge also predicts that the new iPhone will feature a 4-inch screen. That means a change in the iPhone's aspect ratio for the first time.
The device is also expected to use Gorilla Glass 2 which will allow for thinner or stronger glass.
Finally, a new Dock Connector is said to debut on the device. The new port will be a little larger than the bottom speaker or microphone hole on the iPhone 4/4S. It's believed to have fewer pins than the prior 30-pin Dock Connector, perhaps only 16, and the shape of the hole is apparently closer to a pill shape than the prior rounded rectangle. It will be used on all upcoming devices, including an update to the iPod touch that's expected this year, and will almost certainly feature a similarly updated screen and CPU.
iLounge expects Apple will carry its iPad naming convention through to its other devices. ie. "new iPhone" and "new iPod".