Hands free kits were developed so that people could use mobile phones whilst driving or doing something that required the use of their hands. Using a hands free kit whilst driving is alot safer than trying to drive whilst holding your phone. Talking to someone whilst using hands free kits is just like talking to someone sitting next to you in a car.
If you are a business man and you find yourself driving around the country alot but you need to still be in contact with people a hands free kit is essential in your car. You can arange meetings whilst driving, you don't have to try and pull over or call people back. You can get hands free kits for just about any mobile phone on the market.