Cal. Pub. Util. Code § 2885
The commission shall, on or before July 1, 1987, determine the feasibility of requiring that, whenever a call is placed from a cellular telephone, the person receiving the call receive a notification indicating that the call is being placed from a cellular telephone and that the telephone conversation may not be totally private. The determination of feasibility shall include findings and conclusions on the necessity for, and the costs of, implementing a cellular telephone call notification system and on subscriber reaction to the notification system or systems proposed or employed. If the commission determines, in view of its findings and conclusions, that it is feasible for telephone corporations to implement a cellular telephone call notification system, it shall, by rule or order, require telephone corporations operating cellular telephones to implement that system.
Ca. Pub. Util. Code § 2885