"We’re rolling out this feature to U.S. based Gmail users over the next few days, so you’ll be ready to get started once “Call Phones” shows up in your chat list"
After spending nearly a hour trying to figure out why this wouldn't work (including installing the voice plug-in several times) I notice that on the bottom of the google post. I did get to talk to my cousin a bunch though, so it wasn't all a loss.
Can't wait till it does roll out for me though since I use google voice for texting all the time and would like to make and receive calls from it too.