Also apologize for the plug here. I represent the Genesys GETS product which can integrate OCS with your existing telephony infrastructure, without the use of PSTN gateways or requiring that you move to new voice endpoints-- MOC (as a voice endpoint), headsets, or phones. With GETS you can use all of existing infrastructure, including your desktop phones. Our licenses are also transferrable. So, you'll incur no relicensing cost as you upgrade your network in the future.
GETS is a software only solution that can connect with virtually any PBX deployed in the field today. It provides remote call control that is so well integrated with Communicator, users don't even know GETS is there. This is due to Genesys' long expertise with enterprise telephony platforms and our commitment to open systems.
GETS is the only product on the market that can provide OCS telephony integration with over 100 different PBX platforms, across over 25 vendors, and with all PBX generations (IP, TDM, and Hybrid).
http://www.genesyslab.com/products/enterprise_collaboration.asp