https://www.cnet.com/news/sprint-unveils-t-mobile-like-rewards-program-kicks-it-off-with-free-pizza/

To access the program, you simply install the My Sprint Rewards app (Android|iOS) and sign in to your account. Among the perks that are available immediately:

I also found an offer for a free Sprint Drive device (though that's not exclusive to the app or rewards program; it was first announced back in November), a three-month trial subscription to grocery delivery service Shipt and a smattering of other deals.