People call it the "iPhone 5S" based on Apple's pattern of only updating internal iPhone specs every other generation. (First came the iPhone 3G, then the 3GS, then the iPhone 4, then the iPhone 4S, and so on.)
The key differences between the two cases are in the screw placement and in the text on the reverse side of the phone.
We totally fail to see how slightly different screw placement merits calling this a brand new phone. This could be an early prototype of the iPhone 5. It could also be nothing at all.
Check out the picture below, which compares the iPhone 5 to the "iPhone 5S."
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