Today, Skype released a new Skype for iPhone application that finally allows Skype over 3G calls. Only one catch though. There will be a small monthly fee for Skype over 3G calls - even if the calls are Skype-to-Skype. That's a dumb move if you ask me. A jailbroken iPhone can make Skype calls over 3G with no fees through the use of an app called 3G Unrestrictor. I haven't upgraded to the latest version yet because I fear Skype may detect 3G Restrictor and block me from using this functionality any more. I hope they change their minds on this.
Also worth noting is they've added the wideband SILK codec.