See
http://googleblog.blogspot.com/2011/09/launching-google-wallet-on-sprint-and.html

(Thanks for posting Juha!)

http://girisergos.com

<< ...We’ve been testing [it] extensively, and today we’re releasing the first version of the app to Sprint. That means we’re beginning to roll out Google Wallet to all Sprint Nexus S 4G phones through an over-the-air update—just look for the “Wallet” app.
....
Google Wallet enables you to pay with your Citi MasterCard credit card and the Google Prepaid Card, which can be funded with any of your existing plastic credit cards. ...>>

   http://www.google.com/wallet