While pre-orders for the iPhone Duo don't start until October 16, Apple will allow you to prepare on Monday. You'll need to as demand is expected to be high.

It's usually the case that demand for a new iPhone is high enough that unless you're very fast, they go on backorder. You'll still get one, but it will be weeks later, sometimes months, so it helps to be as quick off the starting blocks as you can.

This time, though, the rush is real. Supplies of the iPhone Duo will be profoundly constrained.

At time of writing, the new feature is not available but it is due to roll out Monday, October 12. Once it's live, it will be possible to customize your iPhone Duo even before pre-orders officially open.

From October 12 through late on October 15, you can select your desired accessories, color, carrier, storage option, shipping address, billing address, AppleCare+ plan, and payment method. Some of this has been available since the iPhone Duo was unveiled, but now you can go through every step including any credit checks which normally delay orders, even momentarily.

This pre-pre-order process will shut down at some point on October 15, and then during early October 16, the Apple Store will go down. In theory it will reopen for the iPhone Duo pre-orders at 5:00 A.M. Pacific, 8:00 A.M. Eastern.

In practice, it will be a few minutes late and just how long it will take to reopen depends on a couple of factors. One is location, as this is a global release and different countries can have different waiting times, although you can expect the US to be the fastest.

Then there is also an issue of whether you are using the Apple Store online or on Apple's own store app. There it's never predictable which will open first, so savvy buyers use both.

Which does perhaps seem like overkill. It is unquestionably true, though, that at least most new iPhone configurations sell out incredibly quickly. In this case, with such a high-profile iPhone and apparently such supply constraints, shipping will surely slip back practically immediately.

This is an entirely new iPhone design, though, so perhaps more than usual, it might be wise to try one out in a store before buying. In that case, despite online supplies selling out, stores will have their own stock starting from October 23.