Anderson Patricio writes in his blog about how to broadcast a message from OCS console, please look at his original blogpost to give credits to him.
But i steal the good stuff for my reference.
The first step is to make sure that the user belongs to the RTCUniversalServerAdmins group.
Second step is to open the command promtp and go to “C:\Program Files\Common Files\Microsoft Office Communications Server 2007 R2” folder and run the following syntax and hit enter.
LCScmd /Server /Action:BroadcastMessage /Role:SE /Message:"Type your message here"
Done, all logged in users will receive the message.