In this approach, the Sponsor offers the service to its clients at a pre-set price that can be paid on a periodic basis (usually monthly or annually). Unit cost (cost per customer) is much higher because clients who purchase it intend to use it more frequently. Roadside assistance offered to a membership is a perfect example of an optional model. Typically, an optional program is successful only when the sponsor commits the significant marketing and communication resources that are necessary to ensure sufficient penetration of the program.