California Code, Public Utilities Code - PUC § 742.3

The commission shall, by rule or order, adopt and enforce an operating requirement for coin-activated and credit card-activated telephones available for public use, whether owned by telephone corporations or persons other than telephone corporations, which requires that every telephone display a notice that surcharges may apply to operator-assisted and calling card calls. The required signage shall be phased in over a period of two years beginning on January 1, 1993. A sticker with the necessary notification may be used as an interim measure until January 1, 1995.