You can DL the 7 day trial (skype for the BB) and pay for a little bit of skype credit if you don't have skype setup.
From what I hear the NEW skype for the BB uses only data and does not need the desktop to be running. I have yet to really play with it though and check my tmo bill for certain charges. I will be doing that very shortly and will update. Thanks
BGR posted this yesterday. Confirms what I was thinking. SkypeOut Calls From A BlackBerry : The Boy Genius Report
the comments say something different though. REad em. Kinda sucks.