Small world, but one of my employees' cousins actually work for AT&T customer service/fulfillment, I just had a chat with him and he said that the 128gb is the kicker right now, it's the size that has the biggest back order. He also said the space gray is the most popular color ordered too, so a mix of SG and 128gb is the hard one to get right now. I am not sure how true this info is, again it's what an 'insider' rep told me.
At this point I am just keeping my order in, and when it arrives it arrives. Nothing else we can do about this now. I understand the whole supply/demand thing, but come on Apple, you should have had hundreds of thousands/millions of phones built, and sitting in warehouses ready to ship on release day. I personally know about a dozen people who ordered on or before the 19th, waiting for their iPhone 6 plus' to ship and only know 1 person who actually got their plus (and that was from verizon). So 1 out of 13 people I personally know got their plus (that is not counting the forums/online community of people I don't 'personally' know)