Google announced Monday the extension of a free calling initiative for U.S.-based Gmail users that was set to expire this month. “In the spirit of holiday giving and to help people keep in touch in the new year,” Google has extended free calling in the U.S. and Canada through the end of 2011. The promotion applies to all calls made from within Gmail, and is completely separate from Google Voice, which also affords free calling to the U.S. and Canada. Gmail’s recently added voice calling feature is thought to be a prelude to the eventual addition of VoIP services to Google Voice.