If you looked at the chronological order in which Apple has been naming the iPhone, you will notice that they have a slight tendency to name the iPhone after the iPhone’s sequential age.
As an example, take a look at the reasons for the names behind the previous generation iPhones.
1st iPhone – iPhone – Simply called the iPhone
2nd iPhone – iPhone 3G – The name iPhone 2 was passed over to brand the new iPhone as a 3G phone
3rd iPhone – iPhone 3GS – The “S” suffix was added to signify a faster speed.
4th iPhone – iPhone 4 – The iPhone 4 was called that because it was Apple’s fourth generation iPhone
5th iPhone – iPhone 4S – the “S” suffix was again added to denote faster speed, after the iPhone 4S got a faster dual core processor.
6th iPhone – iPhone 4GS – This could probably be the new name. Many people are thinking that the next iPhone will be called the iPhone 5. However, it wouldn’t really make sense to call a 6th generation iPhone the iPhone 5. iPhone 4GS seems like a more reasonable name, but only if the new iPhone will be a 4G enabled phone.