att family plan question

[HCO]

ok so when you upgrade your second line on a att family plan does that increase your bill each month or does it just lock you into a new contract and keep your primary line price total a month. like my att family plan is 150 a month and that is with a iPhone 4s the primary line and a iPhone 4 that i bought off contract last time so will my bill stay the same every month but the 1st when they add the activation fee or will it still be 150?

thanks for the replys.

 

[cableguy619]

New contract on that number/line and just a ont time activation fee of 36 dollars.