Everyone likes "free" money, and Sprint is looking to take advantage of our human nature with its latest deal: buy any smartphone and add a new line of service, get a $100 Amex giftcard. It's not exactly free money, per se, but it is a nice incentive, especially if you've been considering adding a second line anyway.
As the ad above states, this deal is available for any smartphone (as long as you order it online). You know what that means? That it also works by pre-ordering the upcoming Motorola Photon Q. So if you planned on grabbing a Q and adding a new line for your sister/mother/brother/uncle/dog/self, then now's probably the time to jump on that.