I have a present iP6 with my regular telephone number. I also have an additional phone that was due a full upgrade that I used to order an IP6 S (different number). When my new phone comes on Friday, can I just swap the sim cards and go from there? Or do I have to go into an ATT story and have them transfer the new phone to my old number? I've done this method in the past, but if I can just swap the sim card, it would be easier than fighting the crowds that will be lining up on Friday.