Allright, things are getting a little crazy in VoIP world.
Microsoft's new Exchange 2007 server can be a Unified Messaging Server / Media Server, Live Communications Server (soon to be Office Communications Server) is an Instant Messaging / Presence and SIP proxy and both Nortel and Mitel are claiming to be the 'chosen' ones working with Microsoft.
Nortel outlines roadmap for Microsoft partnership
Microsoft Technology Centers Showcase Unified Communications with Mitel Solution
I think both vendors see the writing on the wall... With 60% of the enterprise mail server market, Exchange is a force to be reconed with. Let's face it, a large portion of that will upgrade to Exchange 2007 at some point. Why, if I have Exchange and have already purchased Exchange CALs and it will work as my VM server, should I go and spend big $ on a different UM solution and fight the integration battle.
MS Outlook owns an even higher percentage as the e-mail client of choice.
Microsoft is trying to position Office Communications Server (LCS follow-on) and the Office Communicator in the same mold. Office Communicator may become the softphone of choice as Outlook is the e-mail client of choice.
It is a pretty easy bet that MS will continue to own the desktop software market. The traditional phone vendor world has also done a terrible job with their desktop integrations. I don't think there will be a question as to whether MS can rule the desktop softphone market and thus drive their server software LCS sales.
I think the question will really be, how long will Microsoft need to keep those relationships around... if they are really even "real" relationships to begin with or just old school vendors trying to hang on to those licensing dollars.