Well, now it's got a new side service that will send you an e-mail when the model you're looking for is back in stock at a local store.
The free service remains U.S. only for now. And in case you're worried about just where your e-mail address is going, creator Mordy Tikotzky tells me he "won't be submitting them" to the National Security Administration. You can, of course, provide some other non-primary e-mail.
All of Apple's iPhone 5S models are currently listed as shipping in October, though it's unclear just exactly how soon that is, here at a third of the way through the month. In the past, the company's provided more detailed estimates, from several days to weeks. Apple's in-store pickup option has proven to be faster for buyers who manage to find what they're looking for, allowing them to arrange a pick up at one of Apple's retail stores the same day the stock appears online.
Tikotzky's tool isn't the only one online. There's also this service, which is also limited to U.S. ZIP codes.