I purchased a new 2012 Sonata. I HAD an iPhone 4S that refused to remain connected to the BT in the car. I took the phone to the Genius Bar at least 5 times. They swapped out the phone and the problem remained. I read the posts and killed SIRI. The phone worked for about an hour, then crashed.
The problem I had was the phone would sync with the car. I could even make a call or two, and even receive a call or two. Then the phone would crash. The only way to restore services was to reset the phone. I use my phone a lot for my work, I also drive a lot for work. So, having reliable BT is mandatory.
Finally, one of the Geniouses at an Apple Store told me the Apple 4S was not certified to work with my car.
The next day, I went to the ATT Store and purchase a new Nokia, with Windows 7.5. It worked perfectly. I could make calls, recieve calls, and I never, ever had any problems. Shortly afterwards, the new Samsung Galaxy S III was released. I traded in the Nokia (within 30 days). I've had the Samsung for about two months? It has worked perfectly. It works with rental cars, my wife's Hyundai, my Hyundai; it never crashes, never fails to answer calls, never crashes, . . . .
It also has a large screen, it is great to read emails/books/Internet searches. I also has built-in capabilities to teather other devices to the Internet on 4g!
I gave my wife my iPhone and I've never looked back.
Problem resolved.