If you'd rather not keep a bluetooth headset plugged into your ear, here's how to cobble together a hands-free system on your dashboard.
Using your phone while driving can be dangerous, but having your hands-free headset in can be just as bad -- especially if it stops you from hearing the cars around you. DIYer scion6tc put together a guide over at Instructables that hacks together a hands-free system that goes through your car's speakers.
For the most part, all you need is a headset from your phone (that you'll take apart), some speaker cables and passing knowledge of electronics and soldering. From there, you can just hit the voice search button on your phone and start talking to make calls. Hit the link to see how it's done.
Make Your Own Hands Free Car System For Your Phone [Instructables]