Free Call to USA and Canada through Gmail.

If you are Gmail user then you can see the "Call Phone" link on the left side of your Gmail account once you logged in. If you click it will take you a page where you will be asked to install the voice and video chat. To install this your PC must have one of these like Windows XP+ / Mac OS X 10.4+ / Linux .
Once you press the install button Google will give you the setup in your download folder. Double click it the program will be installed.
Here you can read the instructions.
Thanks for trying Google voice and video chat!

1. Click OK or Save File in the window that appears.

Don't see a window? Click here.

2. Select Downloads from the Tools menu in Firefox.

A window displaying your downloads will appear.

3. Double click the product in the Downloads window.

Your software will now install automatically. If you need help, click here.

The installer should complete in seconds.
United States (USA) and Canada land lines and mobile phones are free to call.
Other countries are charged like,
India 6 ¢ /min
UK landline 2 ¢ /min
UK mobile 18 ¢ /min

While Sri Lanka operators like SLT and Dialog are worried about the fee calls to USA and Canada as it may reduce their income. Sri Lanka Calls nearly 48,000 minutes to the US daily and to Canada 43,000 minutes calls are made. And most of these calls do originate from Wellawatte, Sri Lanka as Tamil people living there have more relatives there in the USA and Canada.

Source of information Here
Create a Gmail account Link

For you to test the call quality other than Canada and the USA Google is giving US$ 0.10.
To read more about
Call screening
Switching calls between Gmail and other phones
Recording incoming calls
Click to dial with the Chrome Extension
Visit Google voice blog. Here