Just recently, Sprint has reinstated their two-year wireless service contracts as a way of giving its customers more options to choose from. Their options now include to pay full retail price, have a 24-month service contract, pay in monthly installments or even lease the device.
So for example you want to get the Samsung Galaxy S7, Sprint now gives you the option to get the device on a lease (you pay $19.74 monthly), a monthly installment ($20.84 for 24 months), a two-year service contract ($199.99 in two years), or through its full price ($649.99).
By listening to their customers, Sprint has been able to turn itself into the only carrier to provide the most number of choices in order to get a new device.
Source: Fierce Wireless