I just talked to retentions about being able to upgrade on the 20gb plan and he said that if I want to upgrade, I would have to order it through the retentions department. He said if I try to do it at an Apple store/online or ATT, it might change the plan and I will lose the 20gb plan. He also assured me that I was grandfathered in at the 20gbs and they can't just take it away, but a system would not know that and if the plan is changed, they cannot get it back for you.
So i would say that anyone lucky enough to snag the 20 for 10 deal ..and is currently planning on ordering a new phone..needs to call retentions to have them process the order...cuz it was their deal and they are the only ones who know how to put an order thru without losing the plan.....yes it will suck waiting 6 weeks for your iphone plus but until the 20 for 10 becomes a regular plan in the system then its your only choice......maybe in a couple months they will get it sorted out and you will be able to order thru apple ...