Bluetooth 4.0 has a lot better battery life for cell phone. Has a faster transfer rate and longer range
The longer range and faster transfer rate it not need for making phone call and/or streaming music from your car. Better battery life on my cell phone would be nice so I don't always have to charge it while I drive.
I was also told that the sound quality when streaming audio is much better with bluetooth 4.0. But mostly battery life is greatly improved with bluetooth 4.0. Although not very many phones currently utilize it, although it will be the standard for upcoming phones.