I think the majority of people will be absorbed in the game and entertainment. When I go to a sports game it has to be a poor match for me to start laying with my phone. I might check it while waiting in line for a hot dog or something, but the number of people wandering around << the number of people in their seats.
You will essentially have zero cell coverage in the stadium.. iphone / imessage users can use the wifi to send/receive texts... "hey need another beer?"