There are lot's of mobile applications that provide free calls and texts services now.
One and the most downloaded app is
Viber : Free Calls & Messages
by Viber Media Inc.
Viber allows you to call, text, and send photos worldwide for free. Viber is also available iPhone, Blackberry, Windows Phone and many more devices and platforms. Viber lets everyone in the world connect. Freely.
- Free calls with HD sound quality
- Free text and photo messaging
- Ad free
- 100% free
For this to work, you must have internet connection.
You can't send and/or receive text/call when you are not connected.
Moreover, you can only send text messages and/or make a call to your contacts that are also using viber applications.