It works anywhere you have cell coverage (where I live, only Cingular/ATT offers coverage and that's because we're the highest point in the town so we have a tower on our mountain ;) ).
I have the unlimited plan and love it. I know this sounds stupid, but I use Google the most of anything. Especially if I'm trying to get somewhere. I can Google the address and then plug it into my GPS. I also use it a lot when I'm reading to the point where I take it outside with me ONLY so I can look up words I don't know
I LOVE my Blackberry!!! (and I can text so fast I amaze myself ;) )