The device pictured could have a unibody. Apple could have simply used a bonded paint on each ends of the metal back, so the phone would have more "style" than a plain metal back. If the colored pieces on the metal back were glass, it would be incredibly stupid. It's just another point of failure. I think Apple is smart enough to know that having a pure metal back with colored accents would benefit the longevity of the device. It would also feel odd in the hand if the bottom and top pieces were glass and the center of the back would be metal. Just my 2 cents.
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Where is everybody getting this hologram rumor that I keep hearing?
From their posteriors.
There's been no talk of holography from credible sources, and no good reason for it to show up. Apple will have its plate full adding LTE (presumably), a bigger screen, a faster processor and a slimmer build. That's also assuming there aren't any other hardware tricks we aren't aware of.
The way things are going, T-Mobile will have refarmed their 1900MHz service for 3G long before Apple supports 3G on 1700MHz. The sad thing is, the Qualcomm chipset in the iPhone 4S is capable of 1700MHz operation per the spec sheets but Apple has intentionally disabled it.