AT&T iPhone 5 upgrade swap question
Okay, I decided to upgrade my son's Iphone 4 to the Iphone 5 as a Christmas gift this year. I ordered this online from AT&T. Problem is I had to do an upgrade swap from my phone line that has an upgrade eligibility. So, it is my understanding that the phone will be shipped with a nano sim with my phone number configured to the sim. I called Att tonite because I noticed that the email that I recieved after the order indicated that if I don't activate the phone with in 7 days of shipment, then they will do it for me and consequently it will be done under an incorrect number. The guy told me that he will have to call me back in 7 days to prevent this from happening. What a huge hassle... I can't activate the phone when I want too (say Dec 25?) The rep also mentioned that I have to go to an At&t retail store and get a new nano sim card with my son's phone number. I'm sure when they do that, it will disable his current Iphone 4. Are all of my assumptions correct? I'm thinking that the At&t reps are not trained very well and I get conflicting information.
The AT&T instuctions that I see on line for activating Iphone 5 under a different phone number don't imply that I need a new nano sim card.
I'm very confused about all of this. Any advice is greatly appreciated.