For now I'm only interested in the ability to call to the States, The Netherlands and mobile phones for low rates.
A couple of quick tests did give me some problems with sound input and connecting to a Dutch mobile. The connection problem may have been on the other end though. Sound input cannot be chosen through the application (version 0.8.0.2). It should be set correctly in the System Preferences before you start the application.
Audio gain control would also be nice. I sent myself a voicemail through the iSight built-in microphone and the sound volume was very low.