All persons, companies, governmental entities or trust authorities operating an ambulance service within this state may sell prepaid or discounted ambulance service membership subscriptions to individuals who reside within its authorized service area in exchange for payment of an annual membership fee. The agreement between the ambulance service and an individual shall not be deemed to be insurance and shall expressly provide for the assignment of insurance benefits directly to the ambulance service. Under such assignment, the insurer shall be obligated directly to the ambulance service for the lesser of the full and customary charge by the ambulance service or the designated or allowable amount set forth by the insurance policy for any services actually rendered to the individual by the ambulance service during the membership year less any applicable deductible or copayment.