Okla. Stat. tit. 74, § 8501

A. Each state agency, board, commission, department, or other state governmental entity with more than five hundred employees shall develop and implement a system for telephone callback. B. A system that allows the caller to request an automatic callback as part of a menu of options for the routing or handling of the call shall satisfy the requirements of this section. C. The provisions of this section shall be applicable to any entity that uses a toll-free number to allow contact with the agency, and such system shall also provide an automatic callback option and an ability to measure callback efficiency.