I'd guess that depends on the demand for the 4th gen iPhone. Unless it's something *cough* magical, I'd imagine most people won't be looking to upgrade here in the states.
Its going to be quite the opposite.
Let me just say I hate apple but even I have to admit the iphone is a genuis device.
If you look at the iphone from 2g to 3g to 3gs, its not that much of a difference.
Same design, the components inside didn't change that much.
The iphone 4g is a drastic change.
Different design and the inside components are much much better.
From the higher resolutions, faster cpu, front facing camera, better back camera, its a big step forward.
Even had apple just change the design, people would upgrade in bunches just to be different.
Add that to better components inside, the iphone 4g will sell like hotcakes.
I won't be one of them but it will sell.