Personally I think, and hope, that Apple is going to release a brand new iPhone 5. Probably mostly hope, but I think they have a big problem if they don't.
If you look at the competition, almost all the big sellers now have a bigger screen. I know Steve Jobs said that Apple didn't have any plans for a bigger iPhone sometime last year during a conference call, but I also think that the bigger screens have taken a bigger chew of the market than predicted.
As a 3G owner I'd welcome a bigger screen if it's done right. I want a bigger screen with a minimally bigger device. I think the likes of the Galaxy SII are too big, there's just to much device around the screen. I want the next iPhone to still fit in my pocket and at the same time incorporate a bigger screen. Edge-to-edge rumors anyone?
As many others have said I also prefer the tapered edges of the 3G and 3GS rather than the iPhone 4's flat back. I've spent enough time with the iPhone 4 to know what I'm talking about. Without a bumper it's incredibly slippery, and I allways feel like it could slide out of my hands at any time. But then again, the 4 is incredible strong (and delicate/fragile) and feels like it's in a different league material-wise compared with the 3G(S).
If Apple knows which way the wind blows, and I think they do, there will be a bigger screened, slim, sexy, well built iPhone 5 for all of us who are dying to replace our 3G(S) with something from the top of the line (I also hope they will up it from 32 to 64GB, but with iCloud around the corner that's probably unlikely

). For those who just wan't an iPhone I think there will be a new 8GB and possibly also a 16GB iPhone 4(S?). Maybe they will kill the 3GS, or maybe they won't. The 3GS is getting the new iOS 5 update, and I think it will work reasonably well afterwards, unlike the 3G + iOS 4 combination, so it is possible that Apple will keep it alive as an entry level iPhone - maybe a renaming?
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How will the "One more thing"-statement feel if it's not coming from Jobs?