We already know that driving while talking on a cell phone is as bad as or worse than driving drunk, depending on which study you reference. If you are against drunk driving, then you are against driving on a cell phone.
However, I would like to share an article I read that goes farther:
"Incidentally, the increased risk has little to do with your and much to do with your head: It is a cognitive problem, a shifting of your concentration from the road to the call. That many states bar drivers only from using hand-held phones is an act of breathtaking cynicism or dazzling ignorance. They might as well ban only gray cell phones but allow black ones."
Anyone who have ever driven a manual transmission knows that driving one-handed is no big deal.
...so why do we think that headsets make driving any safer? Even more dangerous, it has gotten into our heads that talking on a headset is okay, thus lending us an air of false security.
We've all seen the glazed-over look people get during a phone conversation. When you are talking to someone, your attention is generally on that person (which is why, incidentally, it is not so bad to be having a conversation with your passenger; your attentioin is still in the here and now, instead of far away). Even if you make an active effort to pay attention (usually at the expense of the conversation), all it takes is a few seconds of inattention to lead to disaster.
I know a lot of folks believe themselves to be good drivers while on cell phones, and that's probably true! There are also some people who are better at driving drunk or stoned than others.
So long as you understand the risk to yourself and everyone around you, do what you like.
In the end, as in all things, it is your choice.