I just bought a 2008 528i, I wanted to use the aux input to use my iPhone 4 to play songs from it. My question is, why is that when I plug both the usb and headphone type speaker plug in. I am only able to play songs from the "music" app on my phone.

This is the music app that comes with the iPhone. I want to play music off my other app that I downloaded. Its a music app that u can get off the App Store.

But with both plugs plugged in, it takes me straight to the "music" app instead. If I unplug the usb type plug and leave the speaker plug in, then I'm able to play songs off the alternative music app that I downloaded.

But doing it this way, you can't control the songs from the controller thing and you have to control it manually using your finger. Can I use the alternative music app and still be able to control it off the controller thing?