AutoBluetoot recently got an award, 4 out of 5 stars, from androidmag.de and was printed in their magazine DEZ/JAN 2013.

If you recieve a call, this App will enable Bluetooth automatically and connect to your device of choice. As soon as you end the call, the Application will disable Bluetooth again. This is for example very useful while in a car or if your hands are full.
Bluetooth will run only on your phone if you need it and you can improve your battery lifespan tremendous with just installing Auto Bluetooth.