Programmable telematics systems, methods and apparatus for two-way transmission of data and information between fleet vehicles and a fleet management system. The systems and methods employ a programmable telematics communications unit (TCU) configured to connect to the OBD II port of a vehicle, enabling two-way transmission of data and information between a fleet management system and vehicles in the fleet. The TCU device includes cellular data connectivity enabling communication with the management system through existing cellular telephone networks. The programmable TCU may be toggled between multiple operating modes, wherein the TCU provides different functionality, such that a single vehicle may participate in multiple vehicle programs at different points in time, including separate vehicle rental and vehicle sharing programs.