From reading the story I don't think Skypeout calls will work over 3G, will it? Can any one confirm please - I am no T-Mo!? Just got to see how they are restricting it - as a policy or something technical, inside of the app or the phone.
AT&T network is another thing though - even if it does work, the call quality is going to be absolutely crappy.
Apple restricted VOIP to only Wi-Fi.
So it's an app limitation. If fring submitted their application working on 3G, then Apple would have rejected it.