We're playing with this at the office, pretty slick. Seems like google just
really wants to be skype though 
"Gmail voice and video
chat makes it easy to stay in touch with friends and family using
your computer’s microphone and speakers. But until now, this required both
people to be at their computers, signed into Gmail at the same time. Given
that most of us don’t spend all day in front of our computers, we thought,
“wouldn’t it be nice if you could call people directly on their phones?”
Starting today, you can call any phone right from Gmail." Full info can be
found here