This deal has ended.
Right now at Sprint.com, buy any smartphone and get a $100 American Express Reward Card until 8/26. Check out this Pre-Owned iPhone 4S 16GB for $99 (a price low for a used model by $150) or Samsung Galaxy S-II also for $99 (a price low by $110). Use the gift card and these phones are essentially free! (Just click the "Shop Now" button to see these models.) This offer requires a 2-year contract and a new line of service, and you'll receive the card after 30 days of service. Sales tax is charged in most states.