try this.
{GUIDE} Placing and receiving calls over Wi-Fi using Talkatone and Google Voice
I wanted to contribute to this forum and thought I would start by putting a very simple guide together for placing and receiving calls with the Nexus 7 using Talkatone and Google Voice over Wi-Fi.
As a declaimer: Follow this guide at your own risk. I only mention this because the developer of the Talkatone app does not support the Nexus 7 device. I will add that I have installed this on my wife's Nexus 7 and have had no issue as of this guide.
I would like to acknowledge drsky125 who mentioned Talkatone in another thread and this is how I found out about the app.
The main reason for putting this guide together was I have seen other guides on the web that seemed very complicated. Talkatone has done a great job walking the user through the steps to set this up.
1. Create a Google Voice Account if you do not already have one. This is a very simple process. Just follow this link
https://www.google.com/voice Once you have established your Google Voice Number, you will need to add a couple settings to your account.
A. Select your access number from the left side menu by clicking on the number. This will bring you into the settings page.
C. Select "Phone" tab and check off "Google Chat"
B. Select the "Voice Mail & Text" Tab and check off "Text Forwarding" This will allow you to receive text messages.
C. Select "Save Settings" button to commit these changes.
2. Follow this link to download the Talkatone app from the developers webside Talkatone for Android (side loading version) Scroll down to the bottom of the page and check off "I read and acknowledge the above mentioned limitations" and then select "Download APK" Button. As of this guide, if you try and download the app from Google Play, You will not be able to so because the developer has not included the Nexus 7 as a supported device. For more information check their F.A.Q page.
3. Install the Talkatone app. Once the app is installed, open the app and when you are prompted log into your Google Account. You will receive an email from Talkatone outlining the steps above.