They are convenient, they are time servers, they are wonderful in an emergency and they are a DEATHLY DISTRACTION, while driving. The number of accidents now due to Texting and Cell phone use while driving, is exponential in causing accidents. Hands free are an improvement, but it still a serious distraction to safe driving. But, at least your hands are free and you are not providing blind spots.
As to Test Messaging, which has now become a common practice, it is a disaster in the waiting
There is "NO WAY" you can safely drive a vehicle and do Text Messaging!
Should you consider yourself a prudent user of your cell phone, while driving, ask yourself next time, what occurred in traffic while you were on the phone. Do you have any memory of the traffic and conditions? No, you don't! You cannot perform two functions adequately. You are using the same portion of our brain, when driving or talking on the phone. You are simply driving by instinct.