Hi everybody, I'm getting an iPhone for Christmas (really excited), but I'm curious about activation. My family already has a FamilyPlan with AT&T and I am the third line. When I plug the iPhone into iTunes, how do I make sure it changes my line and not the main one or the second one? Does it detect that we have multiple lines on a FamilyPlan when I enter the account information? Help with this is greatly appreciated, thanks!