Hey guys, I have an AT&T family plan with 2 lines. Line no. 1 currently has an iPhone 4 with the grandfathered unlimited plan. It's not eligible for an upgrade until next May. Line no. 2 has no data plan but IS eligible for an upgrade. I want to upgrade Line no. 1 using the upgrade eligibility of Line no. 2 to an iPhone 4S and give Line no. 2 the old iPhone 4 from Line no. 1. I know I have to put Line no. 2 on a data plan, but can I just order the 4S for Line no. 2 and then swap out the sim card? I don't want to lose the upgrade eligibility of Line no. 1. How do I go about doing so?