Use a cell phone for FM radio?

I keep thinking that surely there is an easy work around for a factory radio that has poor reception. Many years ago a friend of mine had a head unit stolen out of his car, and before he replaced it, he used a portable "walkman" connected to his amp. With that in mind, I was wondering about using a different radio receiver connected to the car somehow.
Has anyone tried using their smart phone's built in FM receiver to see if they can get better radio reception? If it worked, how would be the best way to get the signal to the car? Aux input maybe?

If you're wondering about using cell phone fm receivers, you can go to nextradioapp and click supported devices

"Today’s smartphones already have an FM receiver built in! This means that everyone could have free and easy access to radio for the entertainment they love and information they need, but those FM receivers are not activated by all wireless carriers and phone makers. Listening to radio on your phone using the FM chip instead of over the internet saves you valuable data and battery life. We need your help to send a message that free FM radio matters to you!"