I have read all of the replies and feel the need to reply. Those signs that prohibit use of cell phones is known as "policy" and mean nothing. Notice there is no law number listed that says under what law it's illegal. I sometimes do something called first amendment audit and have educated many federal /state /local officials. In fact there is DHS memo of 2010 that says filming of federal /military facility is legal. If that is legal, using your cell phone to talk and even film is also legal. Basically you can ignore any directive they give and even can flip them off. Lastly remember that us citizens can't be refused access once their identity been established. Many federal employees think their directive mean something when in reality it mean nothing