IPhone 4s on simple mobile? - 1

Hi, I'm searching for a new phone and I have some question about the iphone 4s. My dad will be paying the bill and me and my sister will be buying the phones, but he wants me and my twin to get a phone that doesn't have a contract, because in the past our other phones was stolen by our older sister and thrown away after we got in a fight. So I was wondering if anyone has simple mobile on the iphone 4s. How do you go about putting that service on it. Also can I buy it from Walmart or radioshack and jail break it my self or do I have to buy it unlock from the apple store in order to use simple mobile? If yes, how much does that cost? Also is the iphone as a great as everyone try to make it seem?

Buy the one from Apple which is contract-free http://store.apple.com/...e/iphone4s

Otherwise, I prefer to buy an AT&T iPhone with mint condition on eBay, which should be a few hundreds cheaper then you buy an AT&T IMEI unlock here: http://senseiphone.com/unlock-att-iphone-imei-08294523/