This is pretty awesome. Even before the acquisition you could use a combination of Gizmo5 and Google Voice to get a free phone line, but this could make everything even more seamless.
Well, you could talk for free anyway. Not long after Google Voice started handing out accounts they changed the requirements so you had to have a traditional 10-digit phone number registered with the account.
I was excited by Google Voice and Gizmo because I wanted to ditch my cell phone all together (I use about 75 minutes a month). Once they added that requirement though, I couldn't.