What he is worried about is that they are in fact under no legal obligation to give you that credit because you signed a contract at the higher amount. I agree that this is how Tmo does it and that they WILL give you the credit but you could be held to the contract if they were to insist.
At the same time though, THEIR legal says you'll be paying either 20 or 24 per month after their credit. So they have to stick to that as well.
Mine was available there nearly instantaneously after placing my order. Details on my order in my signature in case they help.
Funny, I bought the same model as you. I just checked again and the order says it's being processed. Not worried. What does your say?