Sprint is running a promotion offering a $100 Reward Card from American Express when you buy any smartphone and start a new line of service. $36 activation fee is also waived. This is on top of the current discounted prices for a 2-year agreement, meaning a new iPhone 4S now costing $149 would be only $49 after the $100 gift card. (The $99 refurbished one would essentially be free.) Sprint has to sell something like $15 billion worth of iPhones in the first 4 years, so it looks like they are clearing out the iPhone 4S inventory..
Valid during 8/14-8/26, online only. Requires 2-year Agreement and new line of service. Account must be in good standing for 30 days to receive card. Card will arrive in 8 to 10 weeks. You can get one $100 gift card per line with a family plan with multiple phones and multiple lines. Android phones like Galaxy Nexus and Samsung Galaxy III are also eligible.
Keep in mind the monthly data plan costs, and don’t forget to add any employee or student discounts available with can be substantial. Compare with other good iPhone options like the Virgin Mobile iPhone $30 plan and the Straight Talk BYO iPhone $45 Unlimited plan.