Sprint is announcing a new program called "Bring Your Own Sprint Device" that is aimed at reducing waste by letting users bring used and inactive Sprint devices to approved MVNO partner carriers. The program will let deactivated and otherwise unused phones be re-activated on MVNOs that use the Sprint network, like Virgin Mobile and Boost Mobile. The MVNO carrier will determine the device's eligibility to be re-activated -- although the requirements have not yet been specified -- and then activate it for use like any other device on the network. Sprint is focusing on reducing the waste associated with the number of phones that sit unused or are thrown away, which could be notably decreased if more used phones can be reused on other carriers.
Another big part of this is increasing the number of devices available to Sprint MVNO customers. Traditionally these carriers have limited device selection to those they sell directly, which aren't always great. If this program is indeed open to all used and deactivated Sprint-branded devices, carriers like Virgin and Boost could lure in many new customers that wouldn't have considered them previously because of their device selection.
Source: Sprint
