Apple App + family plan = 4s ???

So I have a family plan and an upgrade available but not for my line. I know we have upgraded the lines at AT&T in the past with ease using whatever upgrade in our plan BUT my question is
IF I am able to secure a 4s using the Apple App can the Apple store also use one of my other lines in the family plan to upgrade my phone?

Thanks

 

So if my line does not have an upgrade available but my sons line does I cant upgrade my phone at the Apple store?

Meaning I can only upgrade and get the phone from AT&T direct correct ?

Thanks for clairifying that.

 

well if anyone else wants to know... I asked apple and they said if you are the primary person on the accound it is easy. Just put in the # of the phone that is eligable and they will handle the rest when you get there.
So yes you can use the app... Just know what you need before 9 when its updated... grrrr.. plenty available at 9:01 in 7 stores... ZERO by 9:06 lol