I use voice and data together all the time. Speaker phone with long-distance folks while surfing, checking email etc. I bet this will be heavily featured on upcoming AT&T ads.
I agree. I have one particular example where I was in DC on the GW parkway and my wife was back home in Ohio. She needed help with directions and a hotel rental. I pulled the car to the side of the road and from my iPhone I was on the call with her while making a hotel reservation and then giving her directions to the hotel.
I think more people use the voice and data at the same time then we really know.