This has happened to me twice so far in the past month. Both times, I was no where near my phone and it was charging on a flat surface, with no possbility of anything touching the screen. Out of nowhere, an old voicemail would start playing through the speakerphone. I would check the phone and there would be nothing in the status bar indicating that a voicemail was being played. In addition, I set google voice to play voicemails through the normal quieter ear way (not speakerphone). I'm glad the voicemail was just from a coworker and not a drunk friend or anything, since I always have all sounds off (ringtone vibration), including media sounds muted. How could google voice still play it through my speakerphone all by itself?