I have a grandfathered in unlimited data plan, but even if I had a 2 gig plan, I don't actually use nearly that much very often. Most of my data usage is on wif

I have a grandfathered in unlimited data plan, but even if I had a 2 gig plan, I don't actually use nearly that much very often. Most of my data usage is on wifi (when I'm at home, at work, or usually when out at lunch it's on wifi; when I'm on my commute it uses 3G). I don't know whether Amazon's music player streams the music or whether it syncs and caches the music, but if the latter, most of the transfer would probably be on wifi as well.