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I think there are differences in why we wait...

For those without an iPhone, then waiting 4-6 months for a new model may not be a great thing to do if they are tired of their old phone and want an iPhone.

For those like me who have the original iPhone, it makes no sense for me to upgrade to an iPhone 3G just to get an extra 8GB (which still won't hold all my music) and 3G speed. The other features available on the 3G are available on my current iPhone. Now if Apple offered a 32GB version, I would probably upgrade now (new hardware or not).
 
As others have said, we don't really know when the new iPhone will be released. I've got the original iPhone, and it's starting to act up, so I'm just waiting for the new release.

I'd wait.
 
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