California Code, Vehicle Code - VEH § 23125

(a) A person may not drive a schoolbus or transit vehicle, as defined in subdivision (g) of Section 99247 of the Public Utilities Code, while using a wireless telephone.

(b) This section does not apply to a driver using a wireless telephone for work-related purposes, or for emergency purposes, including, but not limited to, an emergency call to a law enforcement agency, health care provider, fire department, or other emergency service agency or entity.

(c) Notwithstanding any other provision of law, a violation of subdivision (a) does not constitute a serious traffic violation within the meaning of subdivision (i) of Section 15210.