Configuring A Multi-Line Receptionist Phone with Sidebox

Can someone direct me to documentation that might give me a better understanding of configuring a Polycom IP 650 with a Polycom IP BEM add on module as a receptionist phone. In their current scenario with the Toshiba system, the receptionist uses the reception phone and sidebox to determine if a particular extension is busy and to do one button transfers to an extension if it’s not busy. Don’t know if that’s possible with an Asterisk system. Thanks in advance for your replies and assistance. I will also talk with someone at AstriCon in Denver regarding this but would like to get started on it prior to that.