You can watch the video above for more details, but according to the Skype blog there's a reason why we haven't seen the update yet:
You may have seen other apps offering calls over 3G, but we're holding ours back for a little bit longer. Why? So that we can give you the very best audio quality we can. When our 3G-capable Skype for iPhone app is released, it'll let you make calls in wideband audio, giving you greater clarity and fidelity – because that's what you expect from Skype.
According to our resident iPhone app aficionado John Herrman, the Fring app already works "pretty well," so I can't wait to see what we'll get directly from Skype. [Skype]