Apple has started sending shipping notifications to customers that pre-ordered the iPhone 4S last Friday. Some orders still say “preparing for shipment,” but most customers have noticed that the iPhone 4S has been shipped with a delivery date of October 14th.

Pre-orders are coordinated with UPS in the US to ensure that shipments don’t arrive before the confirmed delivery date, so don’t get your hopes up for an early iPhone 4S delivery to your doorstep…

Shipping availability depends on the US carrier, but pre-orders from AT&T, Verizon, and Sprint all seem to be at least “preparing for shipment.”

Apple has sold out of initial iPhone 4S pre-order stock, and shipping estimates have been pushed back to 1-2 weeks. Over 1 million pre-orders for the iPhone 4S were placed within the first 24 hours of availability worldwide, breaking all previous records for initial Apple product sales.

You can track your iPhone 4S order from Apple’s account summary page. You can fill out a pre-sign form so that you don’t have to be there when UPS delivers.

The iPhone 4S will officially go on sale Friday, October 14th. Based on initial pre-orders, huge consumer demand is expected once in-store purchases begin. Like a normal Apple product launch, the first people in line on Friday will get to buy the iPhone 4S.

Once initial stock is gone, it could very well be weeks before more units are available.