Iphone Installment Plan?

Do I need to pay the carrier for service/data as well for the Iphone installment plan? I don't use service or data, so I would rather not pay for it, but would still rather pay for the iphone monthly.

You can buy the phone unlocked as you wish.

You pay about 50 percent down, and the rest in payments WHILE ON THEIR PLAN. Or you can buy an unlocked phone at a store, charge it and get hit with all that interest! - and sponge off local Wi-Fi, and have no phone service unless you get VOIP like Skype - and you pay Skype, or only call people for free that have it too. So most of the time, unless you are on free Wi-Fi, you have a chick of metal and glass in your bag - not much works. I know how to work this when bidding another country temporarily - but I do not want to LIVE like this. Consumer Cellular is a good deal. Are you old enough to legally do this?