Why are there never solutions to this kind of problem? It is SO frustrating to find a discussion thread full of nothing but "I have the same problem" entries from users and no solution, suggested fix or acknowledgement from the vendor that they are aware of the problem.
Yes, I have had the same problem with my iPhone 4 and now (ugh!) with my iPhone 5, so it's not a faulty device. In my case I had Apple protection and called support who said they'd never heard of such a problem (which, based on the discussion threads I've seen dating back to 2012 for this problem, is utter nonsense). They had me wipe the phone and re-install all my apps and music from scratch, which sounded reasonable. I do not have any 3rd party music player - just the iTunes that comes with the iOS. The only 3rd party device I integrated it with was a plantronics bluetooth earbud. I specifically did not pair it with my car or any other devices (I suspected my car's Bluetooth might have set up this behavior and wanted to eliminate it as a possible root cause). That worked for a while but. after a few weeks, the problem came back again, so other than a plantronics earbud, everything was pure Apple on the device.
I got a phone call during a meeting the other day, answered it, hung up and suddenly music started blaring - I got a nasty glare from my VP who was not amused at everyone else's laughing as I scrambled to silence it. The iPhone also sometimes starts randomly making outside calls. This is an iOS bug, pure and simple. It's irritating enough I considered removing iTunes but that won't solve the random outbound calling issue. There is nothing I can find on Apple's or anyone's websites that acknowledge this is a problem other than iPhone owners complaining about it and begging for a fix.
Apple - I'm at the end of my rope on this - why on earth are you behaving like Microsoft? I thought you were supposed to be better than this...