The "two-sided" service model (carrier and OTT service/content provider) is seen by many (who do not care much about Net Neutrality) as the definite business model for profitable mobile data services (example - "DT Believes in "Two-Sided" Business Model - OTT to Pay for QoS" - here). We are still not there, but the product infrastructure is introduced, step by step, by the relevant vendors.
"This new functionality, called the DSR Over-the-Top Proxy, enables several innovative business models including “Toll-free” data, where third parties subsidize subscribers’ application usage .. Quality-of-service based tiers .. subsidizes data usage for a guaranteed level of quality, Promotional offers and Loyalty programs".
"Each revenue-sharing model requires a service provider to expose policies that define service rules and subscriber data that personalize services to an application provider. The messages carrying usage data communicate using the industry-standard Diameter protocol. Tekelec’s DSR OTT Proxy adds network intelligence and security functions to the delivery and receipt of Diameter messages. It provides a central point to manage traffic handoffs between operators and applications and acts as a secure firewall for all Diameter traffic coming into operators’ networks. This allows operators to hide the IP addresses of their equipment and prevent an application from flooding the network with a signaling storm of Diameter messages".
See "Tekelec launches over-the-top solution for new diameter network" - here.