Google is looking for beta testers to try out the new Wi-Fi calling with Google Voice! Click on the source link to learn more. You will be required complete a very, very short form with your email address (that is associated with Google Voice). From what I gather, after completion of the form, you will at some point receive notice that you have been accepted as a beta tester and where to download the Google Voice App.
Wi-Fi calling lets you:
Reduce roaming charges when you’re on the go
Keep in touch even when you have poor cell service
Make calls from any device, not just your phone