IPHONE 5 Buy in walmart Some Adice Please?

Ok So I'm thinking to Buy an iphone 5 Soon a at Walmart For 129 Dollers at Walmart But why don't people ever just but the 129 doller one why do People Prefer to Pay 600 Dollers on an Iphone rather then the Lesser Price

Yours comes with a contract, and by the end of the contract you have paid alot more then if you had just originally paid the $600