I have an iphone 4s with iOS 8.1.2 installed. When I am connected to Bluetooth in my car and make a call from the phone's phone book it will switch from the car to the handset each time the call connects. If you press the button that lets you switch between Bluetooth, speaker, or handset you can see it is initially on Bluetooth. If the car is on Bluetooth music streaming from the phone it will even mute and pause the music prior to attempting to connect the call (it will not do this if the stereo is set to anything else). If I initiate the call from the car via steering wheel controls the system works as it should. This is my first iPhone having just come from an LG android phone that worked without problem for calls.
I also had a brief problem with some streaming pausing at each song. I did several things to correct. 1) Reset all network settings, then 2) Reset all settings, and then 3) Turn off iCloud, take the car connection off the phone, take the phone out of the car and start over. That seems to have cured (so far) the music problem.
Also, at no time did it ever drop the Bluetooth connection.
