Looks like if you buy a Sprint Nexus and activate google wallet during the said period, you will get the $10 from Google on the prepaid card as well as an additional $40 from sprint on the google Prepaid card as well.
http://shop2.sprint.com/en/services/popups/google_wallet_50_popup.shtml
http://shop2.sprint.com/en/services/popups/google_wallet_50_popup.shtml