It could use the 3G network to connect to the server to issue the activation command, enabling full data access. The "activation" is a billing formality, not an installation of hardware and drivers to physically enable 3G.
Here's what I know: Home wifi was turned off. Wife went to iPad Settings to turn on 3G. Did not work. Gave a no-data-access error. Got home wifi back on, and iPad on wifi, and 3G could then be turned on.
The implication is that if you're on the road, and decide you'd like your iPad to have data, you're sunk. At least until you can stop at a McDonald's or Starbucks, get on wifi, and then turn on 3G. That's bad design. Maybe it's an unusual glitch that hit my wife's device. I've not spent any time looking into it.












