Next-generation iPhones likely to focus on internal improvements.
Radio Transparent Materials in iPhone?
According to the patent application, Apple suggests the use of Zirconia as a radio-transparent material for part the enclosure:
A portable computing device capable of wireless communications, the portable computing device comprising: an enclosure that surrounds and protects the internal operational components of the portable computing device, the enclosure including a structural wall formed from a ceramic material that permits wireless communications through.
Consideration for radio-transparent material is to allow cellular/mobile phone functionality from the device itself. This is simply further evidence that Apple has been actively considering wireless integration with current iPod devices.
Current iPhone rumors suggest a target date of the first half of 2007 for the possibility of such a device.