iLounge publishes a report based on information obtained from 3rd party accessory/case manufacturers for the iPhone who claim to have received dimensions for the upcoming 3G capable iPhone.
Companies overseas have already started working on products for this one, which is basically the same size as the current iPhone, but has slightly different curves, coloration, and materials. Specs for either or both of these models could be nothing more than disinformation put out to burn developers, but they could also be correct.
Rumors of the new iPhone, however, are being published almost daily now, with several conflicting claims. This latest report claims that the new iPhone will carry a tapered design along the edges, replacing the aluminum backing with a glossy plastic back that approximates the look of metal. The iPhone's front silver metallic bezel will remain, though it is expected to be much thinner. Meanwhile, the overall form factor and screen size is expected to be comparable to the current iPhone, though the possibility of black, white and even red backings is being considered.
The most interesting information in the report is the addition of a 3rd sensor near the earpiece of the iPhone. The existing iPhone houses two sensors (ambient light and proximity sensor) adjacent to the phone's earpiece speaker. The upcoming design is said to have a 3rd sensor in the same location. iLounge speculates that it could represent a small camera, which would fulfill circulating iPhone video-chat rumors, but they also concede that it may be something far less glamorous.
No other details are available, but if this information did come from case manufacturers, you would only expect them to have the raw physical dimensions to allow them to design accessories that could be ready on launch day. Apple has been known to seed certain manufacturers with such information. One case manufacturer even posted images of their cases for the then-unreleased iPod nano a few days in advance of its official launch.