0$ to buy an iphone 4s& 0$ for 2 years contract plan?

I'm not quite understanding what's apple company trying to do, will I be charged something else if I make a purchase on this plan?

The iPhone 4S is free through your cellular carrier if you sign a 2 year agreement with them. If you want to pay every month and be able to not have it active for 2 straight years you would have to buy the phone for the full price of around $200-$250.