California Code, Public Utilities Code - PUC § 7932

(1) If the new area code plan permits seven-digit dialing, provide for a transitional dialing period during which a number in the new area code, or a number in the existing area code, may be reached by dialing either the seven-digit called number, or the area code plus the seven-digit called number.

(2) Subsequent to the transitional dialing period provided in paragraph (1), if prefix codes are available, permit callers to reach a recorded announcement, without charge, that will inform the caller of the new area code when the existing area code is dialed.

(3) If the new area code plan requires 10-digit dialing within an area code, provide for any transitional dialing period or recorded announcements the commission may order.