Activate new Samsung Galaxy with iPhone 3gs SIM card

I have recieved my new Samsung Galaxy S III and need to activate it.  The instructions are not very detailed.  A friend said I should swap the SIM cards from the iPhone to the Galaxy but the SIM card is a lot bigger in the iPhone. 

Is there somewhere online I can go to program my Galaxy SIM card? Or do I need to go to the store? I am in a remote location without access to a store for another two weeks and want to use my new phone! 🙂

Both are AT&T phones.

Thanks