MacRumors came across an interesting change on Apple’s website regarding its how to buy an iPhone 4S section. The updated page now clearly states that the company’s latest smartphone is only available in store by reservation.

Considering Apple’s announcement this morning that it sold a staggering 4 million handsets on opening weekend, the new restriction isn’t surprising. But if you haven’t scored an iPhone 4S yet, you might want to note these new details…

The message on Apple’s how to buy page for the iPhone 4S reads as follows:

“iPhone 4S is available in store by reservation only. Reserve yours after 9:00 p.m. tonight for pickup tomorrow. When you come in, you’ll choose a carrier and plan, and we’ll get your iPhone up and running before you leave the store.”

You’ll be able to place your iPhone 4S reservations from Apple’s website, or directly from the Apple Store application. You can also still pre-order the device from the company’s online store, as well as obtain the device from your carrier of choice.

It’s worth noting that MacRumors has verified that some Apple Stores are still selling iPhone 4S units to walk-in customers, so you might trying call your local chain for verification. But with several places reportedly sold out of the device, a reservation might not be a bad idea.