I'm curious to try this, not that I'll make routine use of it though.
For what it's worth having used Skype and other Voip apps, including Google Voice/Talk, none are worthwhile on 3G. Now on LTE, they are much more consistent. But sadly do suffer in reliability and words dropping out in the middle of calls. What has surprised me is that FaceTime, given it streams video calls, has been much more consistent in my usage even driving 65 mph down the highway (yes I have it on the side, not taking my eyes of the road..)