Audio and chat is completely free but you also have the option to pay for access to more than 10secs of the webcams of Ant and other room members.
Its like a lesser version Justin.tv or Ustream essentially. Bunch of longtime listeners (200 or so most days) of the show use it and Anthony interacts with the listeners by occasionally chatting, using jokes and asking for answers to questions the guys in studio don't know.
If you decide to use it just search for Opie and it should show you the Opie and Anthony Live Room which they use. Otherwise ya can choose view all for the chatrooms and under the Radio and TV tab, then XM radio and the room should be there. For days when Ant isn't in studio (since O&A rarely take the same vacation time) Teds OnA Emporium runs the audio feed.
The room is pretty tightknit, racial discussions take place, etc but my advice would be take a bit to get the lay of the land since they love to give the banhammer to "savages" and people who bug the ladies who cam up.