I agree that your best bet would be to call Sprint. But, you could try checking through your mySprint account online.
1) Under "About my devices," where it shows your name, phone number, and phone model, look to the right of all that and you'll see in tiny, blue letters: "I want to..."
2) Hover over "I want to..." and a drop-down menu will appear. Go to "upgrade this phone."
3) The Sprint phone list shows up and under each phone will be "upgrade discount details," which you can click.
Discounts ranged from $50-$150 off for the 9650 depending on when you upgrade.