Any device that is not currently in the warehouse is considered back-ordered. So until Thursday your iPhone X is in back-order status when the bulk shipment arrives from China to the warehouse.....Texting *6737# says "The items in your order are currently on back order, and we will notify you by email as soon as these items ship."
Odd how it'd be backordered if it went through before launch and there are people showing preparing for shipment after me. Unless it's the model/color thats reliant.
So if it is in Preparing to Ship, that means your actions are all complete and AT&T has completed all processing steps and your order can no longer be modified or cancelled before it ships from the warehouse.
Dave