I was a bit confused talking to an AT&T rep today so I figured to find out the correct answer here:

My question was essentially what the data plan usage really is?
They say it's unlimited data usage.
She said she THINKS it means I can go on the internet whenever I want.
So when I asked if the data plan means I'm hooked to the EDGE and she said she would transfer me to Apple.

I was on hold for 6 mins and than I hung up.