I use my google voice number for almost anything but things that won't accept a VoIP number for registration and account recovery and I give it to them, for a good reason.
So, my default dialer setting is "Ask me every time I place a call". I am mostly happy with the setting since an extra click on the screen is not that big of a deal. Except when I am in my car and trying to dial a number using voice dialing. At which time I have fumble with the phone to click the right position on the screen to place my call.
What I want is, as soon as my phone enters the PAN (personal area network) of my car's audio system (i.e. connects to car stereo using bluetooth) I want my dialer to default to google voice. And revert this setting back when I leave the car and disconnect from the stereo system.
How can I accomplish this ?
EDIT: If need be
OS: Android Nougat
Phone : Motorola Nexus 6