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I do think it's a losing game in general to try to predict future iPhone names. They clearly do not have a coherent or logical naming policy for the iPhone -- it seems to just be whatever sounds good at the time. When they called the iPad 3 "the new iPad," I thought for sure they were going to extend that to the iPhone line and just call this one "the new iPhone." But no. So the next one could be the iPhone 6, or "the new iPhone," or 5S, or the FunFone 5000.

I agree that so far things have been somewhat arbitrary, but my gut feeling is that apple is experimenting with the naming scheme. By introducing this new iPhone as the iPhone 5, I think means that "The new iPad" naming didn't work out so well. The next iPad might go back to iPad 4
 
Maybe they will have some breakthrough with audio on the phone so S could be sound.
 
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