There are more than a few car infotainment systems on the market today as well as a number of smart phone applications that allow users to dictate text messages using their voice. The voice dictated texts can be sent just as any other typed out text. There has been a huge push around the country for cities and states the place bans on texting and driving.
California has passed a new bill called the Freedom to Communicate bill that adds a notable exception to the state's ban on texting and driving. The new bill makes it legal for drivers to send texts using voice activated, hands-free systems. The bill makes it legal for drivers to use devices that are "specifically designed and configured to allow voice-operated and hands-free operation to dictate, send, or listen to a text-based communication."
That means at least in California, hands-free systems such as Ford's Sync and other similar systems are legal for drivers to use. However, there still seems to be some issues for drivers wanting to text using the voice while driving. The law is said to be rather vague on whether or not it's legal for the driver to touch their mobile phone to activate the speech to text functionality. Some interpretations of the law, which will go into effect January 1, believe systems where the driver needs to pick up a device such as the iPhone to activate Siri as being illegal under the new law.