Cal. Public Utilities Code § 742.5

(a) No telephone corporation which operates within a service area shall provide billing and collection services for either of the following: (1) Any telephone corporation which has not obtained a certificate of public convenience and necessity but is required to do so. (2) Any person or corporation providing billing and collection services for any telephone corporation which has not obtained a certificate of public convenience and necessity but is required to do so. (b) Subdivision (a) does not prohibit a telephone corporation operating within a service area from providing billing and collection services for a provider of enhanced service, as defined by Section 64.702 of Title 47 of the Code of Federal Regulations. (c) No telephone corporation which provides billing and collection services for any call placed by a subscriber of the telephone corporation from a coin-activated telephone available for public use owned or operated by other than a telephone corporation shall transmit any charge which is in excess of the maximum tariff rate or charge for that call placed from that telephone, as determined by the commission. Any reasonable cost incurred by the telephone corporation in verifying any such charge may be included in the fees or charges for conducting the billing and collection services. The commission shall adopt rules and procedures for the implementation of this subdivision.