Place calls from Gmail :

You can make a call from your Gmail, from your Google chat list or your emails.

Calling from your Google chat list
The presence of a round green, yellow or red to the left of the contact name indicates that the Google chat service works. If you're using Hangouts in Gmail, you'll see a green or gray circle at the bottom right of the photo of the person concerned. Learn more about phone calls with Hangouts.

If the audio call functionality in Google Chat does not work after the update to Chrome 42, you must use Hangouts to work around the problem.

1-Log into your Gmail account.

2-Google in your chat list, click the Call phone icon.
3-Dial the number to call using your mouse or the numeric keypad on your keyboard.
4-Click Call.
If you have a Google Voice number, it appears on the recipient's caller number display. If you do not have configured Google Voice number, the person you're calling sees appearing a generic number.

Calling from an email
You can make calls directly from the e-mails you send or receive.

1-When you open an e-mail whose text contains a phone number, that number is blue.
2-Click on the phone number contained in the e-mail.
3-Using the keypad that appears, click Call.



Via : http://www.google.com/voice