This is "an official" explanation directly from Steve Jobs as to why Apple is not going to release the white iPhone 4 to public, because the handset just doesn't exist, yes they made a couple of prototypes but never intended to go into production.
So guys stop hoping to own the white iPhone 4 because you are hoping something that does not exist. But the news about the white iPhone 4 has been giving a huge and free advertising for Apple, people are talking about it almost all the time. Like the white iPhone 4 reservations, will white iPhone 4 be released at Christmas and Apple won't release the white iPhone 4 and many more headlines regarding the handset posted by many blogs.
By the way just watch this video from Steve Jobs doll to explains you about the white iPhone 4 and the reason as to why Apple won't release the white model handset:
So forget about the white iPhone 4 guys.