After just a quick glance it looks like its basically doing a callback...
you IM the number and then your phone rings you, you answer and Skype calls the number you sent in the IM....so with the exception of the IM, there isn't really any skype data being sent.

I got really excited as I've been looking for a SIP client for the BB for a while and skype would get me close...but I've always heard that they dont have the processing power for VoIP...

I could also have totally mis-read the info about the app too

This looks a lot like Jajah which does a callback like service...pretty cool stuff. I think we are going to see a lot of these, until the cell providers either A) give us unlimited plans or B) block these services...