Using skype instead of a sip client would have some plusses (extra users! nice interface..) and minuses (closed software, memory hungry, no control on the protocol level for us, fewer possible routes to market).
It would be good to have skype users on board when the system is ready to deal with them and somewhat tested. We will pursue this when we have time/resources and it makes sense to do so. Currently, it doesn't make sense to do so because of limited time/resources and the current state of the skype software and protocol - closed and difficult to use sensibly.
At this stage, since the Skype protocol is closed, it would have to be done using a client that runs on each person's computer - *alongside* skype. This is problematic again, because we don't really want to have to support and maintain a desktop client.
Examples of existing clients that might work for this are: