After Office Communication Server installation, edit the settings using the infomation below. 

Open the main Office Communicator window and press the little down arrow in the top left hand corner.

 Click on Tools and then Options 

 Click  Advanced button on the next screen

 Place a dot next to manually configuration and then enter the following settings:

Internal Server Name: sip.msexchange2007.com:443

Internal Server Name: sip.msexchange2007.com:443

Select the option for connect using: TLS

 Click ok and ok again to compete the process.