Cisco leading in the VoIP market?
I'm sorry, but working at a company which actually does VoIP I haven't even seen VoIP equipment from them. It's not even an issue in interoperability testing. Virtually nobody seems to use them. What I do see are phones from Snom and Aastra, VoIP to ISDN gateways from AVM and Patton, as well as the odd packaged PBX which usually is an Asterisk.
In the backend there is no Cisco except for Routers.
Even in other companies I've seen the market share of Cisco seems to be even below the one of Microsoft. And I don't see it growing with all the bugdoors inside.
BTW quite a lot of companies are looking into Lync connectivity since it can be implemented with some effort and standard SIP software. The question is if it will be worth the effort. It might be a mistake, just like basing your web services on IE6.