In general, Skype works great over the 3G network I am using here at the Mobile World Congress in Barcelona. However, there's one little glitch I've observed that has nothing to do with the 3G network here that Skype might want to take a look at:
Already some years ago I have wondered if interconnection would become an issue with the rise of VoIP based PSTN alternatives. And indeed I can see signs these days of not everything working as it should. Case in point with Skype: I am not able to call my VoIP SIP line at home. Whenever I try I get a "call refused" while just before or after I can call the line just fine from my mobile phone. Looks like wherever Skype connects to in order to reach German fixed line numbers the system is unable to route to a ported phone number. Some room for improvement here!