VZNav is an additional monthly access charge. I use Google Maps or Blackberry Maps. Iheartradio and Pandora are free, they just use your data up. If you have the "unlimited" data plan, you're good up to 5GB of data/month. They don't use as much data as you might think.
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I think VZNav cost around $10 a month, so I deleted it and went with Google Maps/Latitude. It seemed like a smoother app and it had more functionality.
As for the internet radio, I like Slacker above and beyond all of the other stations. You do have to set up an account and what-not, but there is a free version and there are always more stations than I can listen to.
But, to answer your question, like pmhalstead said, as long as you have the unlimited data usage plan, you should be fine with the radio. I use mine all day at work, 48 hours a week. I have yet to even come close to reaching my limit on that thing...