VoIP is not enabled by default, you'd have to set each user to Enterprise Voice and define a Tel URI setting for each account, so out of the box there are no Telephony VoIP features enabled (especially since additional server roles are needed to support the functionality).
You can limit Audio/Video features and Prevent Communicator Call by using settings in the communicator.adm Group Policy template that is supplied with OCS to lock down the settings on the OC client's workstations. You can additionally lock down the client to prevent and RCC or EV calling features (regardles of the user's Telephony settings) by using the
TelephonyMode GPO settings as well.
The GPO template and documentation can be found here for OCS R2:
http://www.microsoft.com/DOWNLOADS/details.aspx?familyid=5D6F4B90-6980-430B-9F97-FFADBC07B7A9&displaylang=en
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS
Disabling Certain OCS Options
