Apple's brief statement re the white version of the iPhone 4:
White models of Apple's new iPhone® 4 have continued to be more challenging to manufacture than we originally expected, and as a result they will not be available until later this year. The availability of the more popular iPhone 4 black models is not affected."
Gee, I wonder why the only model that is for sale is "more popular".
If you were holding out for the white one, get a black iPhone 4 already, enjoy the free Bumper case (through September when Apple may revisit things) and start enjoying the latest iPhone. It's more popular, after all.