You want to demonstrate to a potential client who their users would want to federate with for business processes.
MVP Matt Landis has written a nifty little utility…. http://gallery.technet.microsoft.com/Who-Can-Federate-Tool-a9e00d23
The WCF Tool (who can federate tool) will scan through your Outlook contacts and give you a "heads up" on which of your business partners have public Microsoft Lync or OCS federation enabled. This is a great tool to run for people who do or don't have Microsoft Lync to show them who they could connect with in their own contact list.
Useful, eh? This worked nicely for me – found several on my contact list that I had not thought about.