I gave up and stopped using my Zumo for music (via onboard memory) or iPhone management (via bluetooth). I gave up voice commands from my Zumo but I work fine with visual cues only. My bluetooth just pairs to my phone anymore, which is good because I don't usually have my GPS mounted anyway.
I couldn't do that. I like the audio cues from the GPS, I like being able to keep my eyes on the road and other drivers. Not a big deal in remote areas, but add traffic, dark, rain/snow, road condition, pedestrians, etc, and I like the verbal cues.