My biggest beef with drivers on cell phones is the total lack of coordination that will end up getting somebody killed.
We all know that driving looks easy, but in reality can be a difficult thing to do. I drive like I fly, with my head on a swivel. I'm always checking mirrors, looking over my shoulder, checking blind spots, all to make sure that I am clear on all sides. Hell I look behind me when I'm chainging lanes.
When you're talking on a cell phone or putting on makeup or in some cases even READING (!) while driving, you no longer drive like this. Your SA drops, and your coordination falls into the toilet. Most people I see driving with phones always look straight ahead, and drive with their knees so their other hand can make gestures.
All the accidents I've seen or all the incidents I've come close to having all come from drivers not paying attention to driving. They're more engrossed in the conversation than with driving their vehicle.
Drving without thinking leads to accidents. Cell phones can cost far more than insurence can pay for.
Hang up and DRIVE!