FWIW I called my local BB to inquire about the white model. Should be no surprise that they will happily take your pre-order despite zero knowledge about white iphone availability.
me: Hi are you guys taking preorders for iPhone 4 today?
BB: Yes we are.
me: OK great. As I'm sure you are aware, the white model is not available on Apple's web site. Are you taking pre-orders for the white iPhone 4?
BB: We are not sure about the availability of the white iPhone 4. However we are taking pre-orders for it and telling customers that they are not guaranteed to receive the phone right away at launch.