Once the iPhone goes on sale, Apple

Once the iPhone goes on sale, Apple must manage the flow of orders from people looking for a specific color, memory size and even engravings, said the people with knowledge of the matter. The iPhone 5S will come in three colors and the 5C in five. Online orders are received at factories in China, where workers customize the smartphones and put them on pallets with others destined for customers in a similar part of the world.

"People like to talk about how the key to Apple's success is their products," said Fawkes. "While I agree with that, their operational capabilities, and their ability to scale and bring new products to market efficiently, are unprecedented and a huge competitive advantage."

By monitoring sales from its retail stores, website and third-party resellers, Apple reallocates handsets based on where demand is strongest, one of the people said. IPhones coming off the assembly line in China originally destined for retail stores in Europe could be used to fill a bump in online orders, for instance. The process involves crunching a lot of data.