Switch iPhones from one line to another

[cpt.iphone]

Hi All!
I purchased an iPhone 3GS on one line of my family plan, but I want to use it on another line when it gets here. Is it going to be as simple as switching the SIM cards and plugging it into iTunes??? Does anyone have experience activating an iPhone they haven't bought through Apple or AT&T? Thanks for your help in advance!!!

 

[AiralynRose]

yeah just switch sim cards. the phone doesn't know what line it is supposed to be on

 

[cpt.iphone]

Thanks! I'll give it a whirl when it comes in then.