Make a VoIP a default dialer on Android (for use with Android Auto)

I currently have a Samsung Galaxy S4 on Sprint network and I like how it works with Android Auto on my Pioneer AVH4100 NEX. The major issue I'm having right now is that my phone is relatively dated and in rough shape and all the newer Sprint phones are Spark Compatible meaning that there is no simultaneous data and voice. The main reason I use Android Auto is for the Google Maps function and the problem with the new phones (from what I understand at least) is that when you receive/make a call and the data transmission stops, so will your access to updated directions on Google Maps. This may seem trivial, but if I'm in the car for several hours driving somewhere unfamiliar and have to take calls which may also last a while - it could be a problem. With the Google Hangouts app can receive and reply to text messages in hangouts via Android Auto, but I read that you cannot start new Hangouts (i.e. make a call) and I'm not even sure if you can receive a voice call on Google Hangouts through your DATA connection while you're connected to Android Auto. The only way that I have thought of to get around this situation with one of the Spark phones would be to get AppRadio UR, but the problem is that for the purposes I've laid out above (long intervals of google maps and phone calls) and all that I've read about AppRadio UR my phone would likely not be able to maintain a charge in these circumstances anyways.

Is there a way to make your phone transition to a VoIP dialer by default so that one could be plugged in to Android Auto and make/receive calls via the data connection so that a newer Spark Compatible phone would be useful in this situation? Thanks

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