As of today, it is illegal to simultaneously drive and talk on a cell phone in California, excepting only calls to emergency services. There's no grace period, and under-18s can't even use a hands-free kit. You guys just have to completely shut up now.
One's first conviction gets a $20 fine, while repeat hits are for $50. Administrative fees will be added on top, potentially tripling the base fine.
The law doesn't specifically ban texting, however, which remains under the ambit of driving while distracted.