I had to go out today. I did not connect my iPhone X to Apple play by Bluetooth, nor did I plug it into USB. I had no problems with my iPhone, but I had to answer the phone. Calls did not go through my car. Yesterday I connected to Bluetooth and Apple Play. I could not place calls through my car, I could not use maps, I could not get email or use safari. (I tried these while parked). I received a message each time I tried stating unable to access cellular data. Yet, my phone showed in upper right hand corner it was connected to cellular. Also, cellular was turned on for mail, texts, etc. It also caused my phone to stop communicating to my i watch despite remaining paired. I tried turning cellular off and then back on and tried rebooting my phone. Still not working. Had to totally reset my phone and then my watch. (This was all done after returning home.). Now I am not able to use my iPhone X with my Subaru to play, music, make or receive calls, etc. My iPhone 6 was using iOS 11.3 and I had no problems with the 6 and my Subaru. Very frustrating!!!!