Hmm, nope, does'nt seem to work. For all intensive purposes here's what it says. Guess upgrades don't qualify:
Buy now and save! Get a $50 invoice credit when you apply promo code "SAVE50" to your cart at checkout! This offer is available only through sprint.com. Sprint reserves the right to retire or extend this offer without further notice. A $25 invoice credit will be applied each month for two months for each eligible phone beginning on your second or third month's invoice depending on activation date and/or billing cycle. Offer requires activation of a new device and may not be available in all markets. For new orders with multiple devices on a Share Plan, the invoice credit will only apply to the primary line. $50 invoice credit is not available on iPhone purchases. Nor is it available on upgrades, replacements, add-a-phone to shared plan transactions or the following plans: All Simply Everything (SM) plans, All Basic plans, All Mobile Broadband Connection plans and All Desktop Modem Connection plans. Also, enjoy free shipping when you buy online.