Apple has posted the design schematics for the phone for case and accessory manufacturers with detailed dimensions.
https://developer.apple.com/resources/cases/dimensions/iPhone-5-dimensions.pdf
I figure this will interest others here *cough*Sentry*cough*
It shows antenna areas not to be obstructed by metal, which sort of
confirms reinforces my suspicion that the top and bottom case bands are no longer the cellular antennas and they are now internal.
The reason the iPhone 4 bands were steel was so that the could be used as antenna, the 5 has switched the casing material to aluminum but apple cited it as a poor (or unusable) antenna for the 4. They switched (presumably) because the aluminum is lighter, easier to mill, and as a bonus they could anodize it black.
This then makes me wonder why they have included the plastic spacer gaps if the frame no longer plays a part of the antenna. Perhaps these provide a few microns of flexibility for assembly and tolerance purposes?
mysteries...
EDIT: this could all be a misunderstanding of the material limitations on my part, and perhaps the aluminum end bands function perfectly fine as antennae.