The 3G does have a mic that samples at a higher rate than the 1st gen. I believe the 1st gen mic only has a sampling rate of 8kHz and the 3G goes all the way up to 48kHz. This would translate to better voice quality for the person you're talking to in both regular phone conversations as well as Skype calls over WiFi. However, I am only speaking about the technical hardware improvements, I've never made a skype call on my iPhone even though I do have the app installed.