Activation + Existing FamilyPlan Question

[LWB]

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!

[overanalyzer]

During the activation process it will ask if you're an existing customer and you can say yes and enter your account information and select which line to switch to your iPhone.

[LWB]

Thank you! I thought Apple would have it all figured out.