I pre-ordered from bestbuy as well this morning, but I got there by 12:00 o' clock. They were still taking pre-orders on all models. Bestbuy mobile manager told me these details.
1. You are right. They don't know how many they are going to carry.
2. White ones will be most likely available at launch or very close from the launch day. They just won't have a lot of them. I think apple has them as well, but they are very very low in supplies and they want to just sell them as first come first basis. Iphone 4 white will be very limited, period. I best most of bestbuy will carry no more than 10-15 units.
3. I took my chances just like you did and I ordered 16GB white one.
I paid 50 dollars for the gift card and I will get it on as soon as it comes. I know it's risky move, but you know what? It's better than doing it online.
And at this point, there's no harm. I completely agree.