Update: AT&T has matched this deal. It works basically the exact same way, but you have the option of a 30 or 24 month payment plan.
All you have to do is buy two iPhones (the XS, XS Max, X, 8 Plus, and 8 are eligible, but not the XR), put at least one of them on a new line, and sign up for Verizon’s device payment plan, which divides the price of the phone over 24 monthly installments. Do this, and you’ll receive a $29.16 bill credit each month for two years, or effectively $700 towards a new phone. That’ll effectively get you the 8 Plus or the 8 (at 256GB) for free, or knock a big chunk off one of the newer models.