Use GrooVe IP Lite (free) on your N7. It works in conjunction with Google Voice, giving you a dialer and full integration with your Google contacts. You need an app like this in order to take advantage of the Google Voice calling feature, as such capability is not natively supported on a tablet, like it is on a PC. You could also buy the paid version of GrooVe IP, but besides no ads, only a cell phone can really take advantage of the extra features.
As for Skype, it works just fine on the N7 and is also worth having. Since it's free, you might as well install it.
Also, you can use a Bluetooth headset on both apps to make it easier to hear the person on the other end.
Please note that although I say these apps work fine, they can have call quality issues, especially if your WiFi signal isn't the best.