Not trying to hijack but what kind of headphones do you use? If you're listening to your Ipod and your Zumo wants to prompt you for a turn, does the music go off?
"Not to threadjack"? Sir, you misunderstand this website.

I would lose body parts if I used my wife's iPod. My plan, to the extent I have one, would be to load music onto an SD card and play off that. (But I likely wouldn't, as I'm just not into music and other unnecessary distractions while riding.) What I
had planned was to have wired speakers running from Zumo to helmet; at first, just cheapo earbuds from Radio Shack, but eventually an Etyomics earplug-type unit. However, my wife last night handed me the $50 Amazon gift certificate that my inlaws got me for Christmas (

), so today's plan is to buy the Blueant Interphone, Scala Rider or Motorola HS830 unit and go Bluetooth.
The Zumo allows one to set voice priorities. I think the default is navigation prompts uber alles, so it would step on music or a cell phone call to tell me where to go. (Again, not unlike my wife.)