GrooVe IP play.google.com.gvoip
GrooVe IP is an android app that connects to Google Voice using Voice over IP (VoIP). What this means for you is you can make free unlimited calls to any phone in the US or Canada without using your voice minutes. 

GrooVe IP works on any android device, phone or tablet, and allows you to make calls using the device’s data (WiFi or mobile data) connection. If you have a smartphone with Wi-Fi connectivity but no mobile plan, you can use this app to convert it to a free, full-featured working phone.

This app has a separate dialer that can be used to make calls. Alternatively, the native dialer, call-log, contacts, and favorite functionality can be shared between the phone and app on a call-by-call basis.

Notes:

• Please ensure that your Google Voice account is associated with either a gmail or google apps account.
• To receive incoming calls you MUST go into your Google Voice account and forward calls to Google Chat.
• GrooVe IP uses 1.2 MB per minute during a call

For requirements, setup details, answers to frequently asked questions, known issues, or more information, please visit http://snrblabs.com/snrb/grooveIp.aspx

If you have any questions, feature requests, or run into any problems please contact us! We cannot help you if you only leave a comment.

What's in this version: (Updated : Aug 24, 2013)

• If you are having trouble with an update please try a clean install. Uninstall the app, restart the device, then download and install the app again.
• Fix duplicate SMS
• Add ability to delete SMS
• Fix SMS screen stuck at unauthorized
• Fix SMS notifications
• Allow copying text from SMS
• Linkify SMS text
• Add higher def laucher icon
• Stability improvements and bug fixes

Required Android O/S : 2.1+

Screenshots :