“In a case the iPhone 3G looks nearly identical to the iPhone. It has the same chrome trim around the huge glass touchscreen. The circular indent of the home button still lies below the display, and above it is simply the earpiece. There are still only three buttons along the sides; at the top left is the switch to silence the phone, with the volume rocker just below it, and at the top on the far right side is the lock button. The dock connector and speakers are at the bottom, and at the top left of the back is the small 2 megapixel camera.
There are differences though, most notably is the back housing. Gone is the metal with the black plastic bottom, replaced with glossy plastic in a black or white finish. The white is only available on the 16GB version; you can get black on both the 8 and 16GB models. With the silver finish gone, the side keys have been changed from black rubber to silver metal. It’s a small gripe, but the key edges are rough and while it won’t cut you, running your fingers over them isn’t a smooth experience. The speakers at the bottom are much smaller, and like the earpiece are covered in silver metal mesh rather than the previous perforations.
Overall dimensions have actually increased, though the 0.5mm thickness difference is offset by the rounded edges of the 3G. ” Read more here: