Lets say I just walk in....



Okay I am kind of confused about some stuff and I'm sure a lot of people are.

I am on a family plan, 3 people. Now, I am elligable for an upgrade with my phone but the other two aren't. I know the prices are the same for the iPhone with an upgrade or not so I'm not worried about that. Now, lets say I went into the store tonight and bought one iPhone. I buy it for $535(included with tax cause I already called and asked) and I come home and plug it into my PC and go through iTunes to activate it? They told me I need a valid credit card to activate it...Why? Will this charge anything to the bill? And after that, how will it know what my number is and everything so everything will work fine? I don't understand?

When it signs the 2 year plan, do I gotta pay for or can I just keep the same plan I am on and not do anything else to it? Is there an actvation fee? Some one please answer this...thanks.