In short, yes, even though the N7 doesn’t obviously have phone-related user interfaces, you can use the N7 as a phone for both outgoing and incoming calls via VoIP, and this can be accomplished completely for free via Google Voice accounts.

The fairly easy steps:

Obtain and install the GrooVe IP Lite (GIPL) app via Google Play. This version is free and has everything you need for this situation. You still might wish to purchase the full version for $5 to support the fine work of the developer.

via Lauren Weinstein’s Blog: Using the Google Nexus 7 Tablet as a Phone, For Free (+ a Privacy Hint).