Okay so I have a 2nd gen iphone & I wanted to know how to activate it. I have AT&T but it's not the original SIM that's in the phone right now. Basically it's my old SIM that has my old number that was used to activate the phone. I don't want to add the iphone data plan to my family plan so how can I activate the phone without AT&T knowing its an iphone?

I'm so new at this.

Thanks for the help!