Even though I am not worried or concerned because I know it won't change when I get my phone next Friday, I am always curious on the process of when and how everyones orders change to preparing, etc. Obviously not order of when they received the order as my order went in exactly at 8:00 am EDT.
My take on the whole workflow for a typical order is that once you place the order, tasks like credit card holds are put into place, the phones are then assigned to your order where the serial number and other properties are recorded. These logistical tasks are considered "Processing".
Once all of that is completed, then the shipping strategies are formed...grouping similar destinations, creating shipping labels (and, thus tracking numbers), physically inserting the products in shipping boxes and assigning to shipping pallets, etc. These are considered, "Preparing to Ship" status.
The pallets are picked up for their trip to the airport. They typically travel from China to World Port in Louisville or Nashville via FedEx. Once they arrive there, they are scanned by the transport company (UPS, FedEx, for example) and then your order status changes to "Shipped" and then you can explicitly track your package from there to your local distribution center where they are put on delivery trucks bound for your home (or other final destination).
Also, your product may arrive in the U.S. earlier in the week, but they will lay dormant until the night before your delivery date. At which time, it continues its journey to you.
There are many other steps I omitted (going through U.S. customs, a layover in Anchorage, Alaska [gotta refuel the airplane]), but those listed are the gist of it, in my experience.