Office Communications Server - No PBX, really?
A PBX is not required. It is possible to use a native OCS environment for all call handling. The OCS Mediation Server with a gateway will connect to the PSTN. You can find out more information in the following two documents:
Integrating Telephony with Office Communications Server 2007
http://www.microsoft.com/downloads/details.aspx?FamilyID=F18A27AB-E790-4602-A3B2-A56888DD3DDF&displaylang=en
Office Communications Server 2007 Document: Enterprise Voice Planning and Deployment Guide
http://www.microsoft.com/downloads/details.aspx?familyid=24e72dac-2b26-4f43-bba2-60488f2aca8d&laylang=en&displaylang=en
