AT&T is quietly running a Next upgrade promotion that will reward existing customers with a $50 bill credit when they trade up to a new iPhone at an Apple retail store or through Apple's online sales channels. Customers can now finance the iPhone 5c, iPhone 5s, iPhone 6, and iPhone 6 Plus through AT&T Next 12 or AT&T Next 18 plans and receive a $50 credit on their wireless bills.
To receive the credit, the iPhone must be purchased as an upgrade on an existing line and be financed through AT&T Next. The phone must be on Next for at least 45 days and AT&T says it will credit your bill within 3 billing cycles. You can always pay off the balance of your Next finance plan after that should you wish to avoid continuing to make installment payments.
The promotion runs through the end of the year.