There are no other open world areas to explore. There's just virtual Steelport. The other areas are mission based, like deckers.die from SRTT. One of the things I really tried to stress to the Volition guys while I was there was the importance of being able to revisit those other areas and simulations post-game so you have more places to explore and mess around in. Of all the input I gave I really tried to hammer that particular idea home.
Well, that's kinda disappointing. Although I was only really worried about this because it didn't look like they expanded/changed the city a whole lot from the first couple of trailers.