Someone on the inside at Best Buy decided to leak a "mini launch guide" with iPhone 4 information for the store. Just because you pre-ordered the device for the $50 they were asking, does not mean you will get it on launch day.
The guide says "inventory quantities are still being determined" even though it was announced that each store would receive 45 units. It continues to talk about how the units being in the system is correct, but employees cannot make any promises to customers when they will be available.
Hopefully, at least some of the customers will get what they ordered on time, but at this time, we don't know. Next time you should avoid going to a store that can't use proper grammar on one of the biggest launches of the year, hence the "Reserve your's Today" slogan.
Guide Scans:
Scan 1
Scan 2
Scan 3
Scan 4
Source: ModMyI