California law doesn't prohibit the usage of cellular phones while driving a vehicle as long as the driver is over the age of 18 and is using a phone with a hands-free device. Usage of hand-held phones while driving is banned in the state. In Arizona, a law is on the books that bars distracted motorists from operating a vehicle. It's up to the law enforcement officer's discretion in each case as to whether to a cellular phone is being a distraction and whether or not to issue a ticket. In both states, it's illegal to use a cellular phone to write or send text messages while driving.