Drivers behind timing of shipment
Based on what I know about AT&T (and large corporations in general), the seemingly illogical shipment schedule is almost assuredly being driven by accounting and internal business processes.
AT&T wireless is divided into regions, and each region into divisions. It's not like its really FIFO for orders nationally. Its FIFO based on region, with further subdivision based on on business unit (online, Premier, brick and mortar). So there are a large number of queues that are fulfilled each day, each pulling from a pre-assigned inbound inventory. I am sure there is a bit discretion between queues, but probably not much.
Each manager for each region/division/business unit will be measured (and bonused) based on performance, so they would have little incentive to "share" their inbound inventory. ****ed up from a consumer standpoint, but almost assuredly true. Complaining to the president's office would get some results, sometimes, as I am sure his office has an allotment of devices to take care of escalated issues.
Further complicating the mess is the whole NEXT program. That is, pure and simple, a revenue recognition play on AT&T's part. Sell a phone at a subsidized price, you can only recognize the price you sell it for, not the retail price of the phone. Sell it as a NEXT device, they get to take the entire retail price of the phone at time of sale as revenue. Boom- every NEXT device is worth 2x as much to their bottom line. I bought mine as a NEXT device, and it has aways shown as "Preparing to Ship" as status, since 10/26, never backordered. Lets them recognize the revenue immediately.
All the above is my opinion, I have no inside info, blah, blah, blah. But based on the the way publicly traded companies are operated, it would surprise me if that's not what's going on.