Thanks to Zero1 over at mess.be for this:

Some of the new features that have been incorporated in this updated version are the ability to add people, start a conversation, start a video conversation and start a voice conversation via a link in a webpage. The links are constructed as so:

Start a conversation: msnim:[email protected]
Add a contact: msnim:[email protected]
Start a voice conversation: msinm:[email protected]
Start a video conversation: msinm:[email protected]

Some people may notice this feature is similar to AOL Instant Messenger's link system. However, people who remember the workaround that was made for MSN Messenger 4 & 5 will appreciate how much simpler this is to implement in their own webpages.

Also, the quality of audio over MSN Messenger has been improved and better echo-cancellation implemented.