TV Answer Man has confirmed that the list of TV providers that will offer the free preview include Dish, Sling TV, Optimum, and Frontier FiOS. However, more providers are expected to join in as well so consult your on-screen guide for more information.
Swanni-
Dish, Optimum to Hold Free HBO Preview - The TV Answer Man!
Swanni-
Dish, Optimum to Hold Free HBO Preview - The TV Answer Man!