Google has announced it is extending its free Gmail calling deal for another year, allowing desktop users to make calls to any domestic number within the United States or Canada through the end of 2012.

The offer has been available since August 2010 when Google introduced the ability to call mobile or landline phone numbers right from within the Gmail's chat interface, powered by technology from their Gizmo5 acquisition in 2009.

Although at the time it was said the free local calls offer would stand for the rest of the year 2010, Google has kept it running ever since and plans to continue doing so for at least another 12 months. It may be that they're focused on growing the user base in order to become a serious contender against Skype, or perhaps the company is making enough revenues form international calls to subsidize the service.

Google Voice users can accept incoming calls through desktop Gmail at no charge. Those outside the U.S. still have to pay for all of their calls at what Google calls "insanely low rates," starting at $0.02 a minute.