Now that Apple has released the iPhone 6 and 6 Plus, I feel that it is time for Apple to re-think the way they brand their iPhones. Apple likes to keep things simple, so I think that Apple should simplify things and drop the numbering of the iPhones.
Apple stopped numbering the iPads, and they don’t number any other hardware products that I can think of. None of the current Macs or iPods in Apple’s lineup have numbers in their names, nor should they.
The iPhone lineup has traditionally sat at very specific price points, and it makes sense for Apple to keep the iPhones at those price points.
And now that Apple has clearly defined the iPhone lineup with two high-end iPhones and two low-end iPhones, here is what I propose/predict for iPhone names in the hopefully not-too-distant-future (all prices assume a contract with a U.S. cellular carrier):
"iPhone C": free (low-end, 4" display, multiple colors)
"iPhone S": $99 USD (low-end, 4" display, gold/silver/gray)
"iPhone": $199 USD (high-end, 4.7" display, gold/silver/gray)
"iPhone Plus": $299 USD (high-end, 5.5" display, gold/silver/gray)
And every year, these names could stay the same, regardless of any hardware changes. This would give Apple the freedom to break the ‘tick-tock’ cycle of form factor changes every two years. And this would also allow the 4” iPhones to stick around indefinitely, as I am sure there are many people who prefer the 4” size over anything larger.