Free speech zones in U.S. How far can they go?

http://digg.com/newsbar/topnews/occupy_wall_street_protesters_asked_to_kindly_stay_in_the_first_amendment_rights_area

"According to an updated map on the website for Federal Hall, as pointed out by Gothamist, demonstrators will be asked to stay on one side of the big George Washington statue — he was inaugurated at the building — in the 'First Amendment Rights Area,' a.k.a. 'freedom cage.' Visitors can enter from the other side, steering clear of the riffraff."

There are areas that have been designated by our court system that are MORE free speech zones than others.  Public sidewalks are pretty much all free speech zones.  Private property is not.  But how about sort-of-public places like malls?  That's a bit trickier (see Pruneyard case about that).  The courts weigh private property concerns with a Constitutional free speech right.

Also there are possible time, place, and manner restrictions that can pass court muster, if the government can give a compelling argument why free speech should be restricted.  Some states have laws that you can't protest at a private residence, for instance.  If some group has a parade permit for a designated street, there could be more restrictions placed on others' free speech during the parade.  So, it's not all just cut and dried that you can protest wherever and whenever you want.

All that being said, I'm not sure why in this particular case the government wants to make a little box where free speech is ok.