If you were thinking about switching over to Sprint, you might want to consider doing it before August 26th. Sprint is offering anyone who purchases a smartphone online (with a 2-year agreement) a $100 reward card from American Express — as long as they add an additional line of service. It’s certainly not a deal that’s going to cause a mass exodus towards Sprint, but if you were already headed that way, you might as well get yourself an extra $100.