If it following naming conventions it will be the iPhone 5, which will have a different form factor... then the next model will be 5S and then 6 and then 6S, until we all die.
It'll either be the iPhone 5 or the iPhone 4G. Probably.
iPhone 6 would be my guess.
but if they introduced a different class of device like they did with the iPod line then maybe i can see another type of name.
though the iPhone SE (Steve Edition or Special Edition) would be interesting.
iPhone 5 SLP=Steves last phone
It is interesting that Apple are using release numbers for the iphone, however the cycle we have seen has been based on the product design; the difference between the 3g and the 3gs were the internals not the form, the same with the 4 and the 4s. I would be expecting a similar release with the v5 case and then a year later the 5s with better internal specs.
SJLI-Steve Jobs' Last iPhone