Rich does a very good job of telling us all about the new features found in Skype 2.5. While he's been typing away I've had a few in the know tech types tell me more about SkypeCast.
A SkypeCast entity is a special phone number
When parsing this, you ignore the skype: that is the protocol handler for telling the browser to launch skype.
The + indicates that it is a full international phone number. The first 9 indicates that the number should reside in Asia. However, 990 is actually an unallocated country code. So they are then trapping the calls at their PSTN gateway and sending them off to a normal conferencing bridge.
I also learned that users are placing a SkypeOut call to a normal conference calling bridge. The person who originates the call is the moderator. For now, they are NOT charging you minutes to use the service, but could vary easily make you pay SkypeCredit to call it.
Interesting isn't it!
Alec has more on the way it's done.