I place blame on Apple and T-mobile for the issues with the Plus not being available.
Apple: I'm reading that they didn't anticipate the black/jet black Plus to be as popular as it is, or the 7 would be this popular. Here is the fault with that argument: There are NO plus phones in black or jet black anywhere. Normal production would have produced some of them, but it is almost as if they didn't make ANY in time for the launch. Noting it was available for pre-order when the product is NOT available at launch is deceptive. They could have easily noted in the Keynote that the Black Matte and Jet Black versions would be available in October, and then if supply was available, send it earlier than the estimate. I don't know of anyone who would be upset getting it earlier than the shipping estimate, but they surely will be if it is late.
T-mobile: Not being able to handle the numbers. The system crashed at 12:15am on the 9th and many, many customers could not pre-order. Then promises were made and not kept about phones being available on launch when it was not confirmed they would have the product to satisfy those pre-orders. In my lowly opinion, when T-mobile noticed a problem with supply and demand, they should have released an email to those customers (or text) noting what is going on: let your customers know we initially were told we would receive them in time for the launch, but Apple has delayed delivery. In my opinion, transperancy is key, and while you will not please everyone, having CSRs saying different things to customers in the age of social media is not an effective communication policy. Just be honest, and upgrade your IT!
Stepping off soapbox.