Today a new OTA(Over the Air) update became available for the Nexus S 4G, this update (Android 2.3.7) brings the much awaited Google Wallet feature to the Nexus S 4G for effortless payments. If you haven’t updated your phone yet, go to settings –> about –> system updates and update to the latest available firmware. Currently Google Wallet service is exclusively available on Sprint Nexus S 4G.
Google Wallet for Android Video
Google Wallet will work with American Express, Visa and Discover for now. You have to set those up in your Wallet then you can easily make payments using only your phone.
via Google blog.