Does activating your iphone cancel your current plan for at and t?

Okay, so my father and I just upgraded two phones in order to get two iphones. My Iphone came in but not my father's. I was just wondering what would happen if I activated my Iphone before he does. Also, does it cancel out the current contract we have now or what?

Activating a phone never cancels a contract.

Either you already have a contract and the phone you're activating replaces the previous phone that was on the same contract (so your contract doesn't change)…

… Or you're activating the phone at the same time you're starting a new contract (this also happens when you upgrade your phone after your old contract ran out).

Be careful that you aren't getting another contract when you already have one! That probably wouldn't happen if you bought your phone from the same phone company you're already using, but it might happen if you don't know what you're doing and you buy from a different company.