According to [You must be registered and logged in to see this link.], iPod touch 5G Images have been leaked in the wild with non-physical home button button. The device is running firmware 4.2.1MC14, carries 128GB storage and is marked model MC550LL. The device also has aluminum back, which is rumored to exist on the unreleased iPhone 5.
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Marked with the "DVT-1" badge found on the earlier examples of the iPod Touch discovered in 2010 that sported front and back cameras, this model has 128GB of memory, is running firmware 4.2.1MC14 and is marked model MC550LL which points to a Mac Pro model as well as a permutation of the 4th Gen iPod Touch.
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Its thought the perhaps the device could be a prototype or tester that made it into the wild.