I think that it could be interesting to allow the use of Car Audio systems for calling and receiving calls. What stops me using this phone as an alternative to a dumb phone is this issue.

PS: I actually have followed recommendations and I have bought a polarcell battery replacement.

The car audio is connected via BT. Some devices with newer BT version cannot connect to the S2. What I recommend you is, install only the android base (don't flash the sfos zip) and boot into it. Try to connect android to your car audio system. If it connects and works, then probably there is a problem with the BT settings in my port. If it doesn't work, then obviously cannot be easily fixed on the Sailfish Os side either because the problem is on the android side.

I report that Car Support is working properly with Cyanogenmod 12.1 on the GT-9100. Must be on the SFOS part of the wall.

PS: On the other side I wonder if Replicant can be used as base.
https://redmine.replicant.us/project...laxySIIGTI9100

I have tried Replicant on the GT-9100 and I am able to use bluetooth and to connect to a Parrot CK-3400 but I am not able to hear any sound. With SFOS 4.4.0.72 I am also able to connect properly to this Car System but it seems as if audio is not routed properly. I am going to try again with CM-12.1 because maybe my previous reply wasn't 100% accurate.

OK, now I can conclude 100% sure that GT-9100 can make and receive calls properly with audio routing on a Parrot CK-3100 and on a Car Multimedia from a Toyota Hybrid from 2014 using CyanogenMod 12.

I had been using Replicant on my S2 for a while. It crashed a lot and failed to install many apps, so, finally I replaced with my own built Sailfish Os.

Regarding you car multimedia:
Yeah, probably the routing is not correct. Unfortunately don't use car multimedia with my phones, so cannot really test what the correct routing should be.
What I can advise you, install a Sailfish Os app called Audio Output Chooser from Chum and try whether you can route the sound properly to your car multimedia. Then, post your test results here if that helps others.