Just to add to Si's response ... what will normally happen is that when you place the order, a hold will be placed on your card for the price of the phone (plus AppleCare if you get that, which I always do). Your card won't be charged, but if you check your balance it may show the lower amount. The hold will be lifted after a couple of days.
Your phone will be shipped — and your card will be charged — in time to arrive on October 26, the same day the new model goes on sale in retail stores — if you've placed the order before the initial pre-order batch has sold out. (There will still be new phones available at retail locations, on a first-come-first-served basis, until that supply runs out.
A fun thing to do is to use the tracking information from Apple to follow your phone as it moves across the world to arrive at your door on release day.