I just read in a thread that reserving your phone online does not guarantee it? What is the point then?
The point is that there are a lot of steps to buying an iPhone, and most of then can be done online -- before you walk into an Apple Store.
1. AT&T has to verify that you're eligible to buy an iPhone.
1a. If you're new to AT&T, AT&T has to run a credit check on you.
1b. If you're an existing AT&T customer, AT&T has to figure out the iPhone price for you (which depends on where you are in your contract)
2. You have to pick (re)select voice + text plans.
3. You have to agree to AT&T's terms and conditions.
Apple's online process lets you finish those 3 steps in advance, which can save you A LOT of time in the store.
If you walk into the store to buy an iPhone and you DIDN'T do those steps in advance, then an Apple employee has to do them for you. This involves them typing the answers to all of those questions into their little EasyPay PDA device. There's about 3 or 4 screens they have to fill out, and between each screen, their EasyPay sends the data to AT&T for confirmation and waits for the response back. This adds all sorts of extra time to your purchase. On "launch day" last year, this process failed frequently, causing EXTREME delays. So if you have the chance to do it in advance, I'd highly recommend it.
If you want a guaranteed pre-order, either go to an AT&T store and sign-up there, or do the order online with Apple and avoid stores all together. Their website says your iPhone will be delivered on 6/19.