As of midnight, Californians are required to use a hands-free driving system in cars. This marks the largest hands-free driving initiative in U.S. history.
While local municipalities in California have seen this as a potential ticket/revenue generating exercise, the California Highway Patrol does not. The CHP has said that they will not (at least initially) be pulling drivers over for lack of hands-free. However, the CHP has also said that they will ticket you if you aren’t using hands-free, and violating some other driving law.
California’s hands-free law requires an hands-free system that does not involve touching the device to operate it. This includes Bluetooth, in-car systems, and wired headsets. In addition, you can also use the speakerphone function of the device, when combined with voice-activated dialing.