Cancel pre-order to buy in store?

Right now, I have a pre-order for the iPhone 4 through apple that has a ship by date of July 14th. If one of my local stores gets a phone in stock before then, will I be able to cancel my pre-order and be eligible for upgrade in the store? OR, can I go in and buy it for the upgrade discount price without canceling the pre-order online, as not to loose my place if I don't get one in the store, then just cancel it online when I get home?

Thanks in advance!

p.s. - sorry if this is the wrong place to post in!