The rear panel remains. Looks like that leaked shot was reasonably accurate.

Unlike the metal rear panel on the original iPhone, the rear panel appears to be made from ABS plastic. The coat on the back feels nice and is very reflective, hopefully it's durable as well.

There doesn't appear to be a serial number on the back panel of our phone. We don't know if that's unique to our phone, or true with all 3G iPhones.