You guys do make a good point about iOS 5, because the iphone 4 will also get it it will still be a updated/current phone.
But it will probably not be considered for the next version of the iOS but that might also take some time to happen.
Now other question that doesnt completely relate to the thread, but for the ones who have used a 4" screen to type and the used the 3.5" of the iphone, did you noticed a big difference? I have seen some videos comparing screen and it seems that the 4" is more "taller" than wider comparing to the iphone.
I bet it will
If 3GS works with ios 5 then I'm damn sure that the iphone 4 will work with the next IOS update