Build VoIM into Microsoft.
Developer ecosystem attack.

Microsoft could choose to commoditize Skype's Voice Over Instant Messaging (VoIM)market. This might be part of competing with eBay and PayPal or just to defend their own messaging products. 

Microsoft supports more than a million programmers.

Part 1. Tools. Microsoft can publish tools to make it drag-and-drop easy to build your own skype clients, build it for your own apps, social networks and web services. 

Microsoft could do this for Windows Vista, Windows Mobile, Office, web and Xbox gaming platforms. Each tool brings in hundreds of developers. Each new third-party app those developers build in turn ties up thousands of potential Skypers or convinces them to switch.

Part 2. Turning Microsoft messaging clients into platforms. What if Microsoft published their own set of standards for the stuff that enables Skype?

• IM/chat/microblogging
• voice calls/conferences/spatialization
• video calling/conferencing
• encryption
• presence
• identity
• file exchange
• people search

MSFT doesn't need to be inventive: just adopt existing standards. Microsoft's de facto power could force Skype to change and open its architecture before it is ready. 

Part 3. Alliances. Microsoft enjoys limited partnerships with telephone companies. There's no reason those partnerships might not extend to making Windows operating systems, servers, applications and networks "Skype-hostile" and "incumbent friendly." 

Part 4. Adding talk to Microsoft's online properties. The technologies for embedding live conversation (text, voice, video) in web pages has been here for over a year. Microsoft's web properties draw so much traffic that "talkifying" those sites could

1. Stifle user adoption of feature rich, fat (bloated?) desktop clients like Skype
2. Define Microsoft's technologies and partners as standards, and
3. Convince leading web sites to follow Microsoft's lead and use Microsoft's tools, not Skype's.

So far the only thing holding back Microsoft is Microsoft. I predict there will be an hour when Microsoft decides that mobile and Internet telephony, videophony, conferencing, and live messaging directly affect their corporate strategy. One minute later: Microsoft will point their high powered attention to the problem . Two minutes later: everyone else will have a strategy for partnering with Microsoft or carving out a niche.