Indeed. We have used multiple OBI 110 boxes, connected to different Google Voice numbers, and it works like a charm for landlines. Free landlines. As many as you need. For free calling, with a regular telephone.
I'm sorry, but anybody who knocks a service that allows you to deploy free regular telephones (after the cost of OBI 110, $47 on Amazon) to anyone with an Internet connection isn't seeing the forest through the trees. Not everybody has or needs a mobile phone. (And especially the cheap phones many people buy as emergency phones for their senior parents are absolutely crap to talk on.)
As long as Google doesn't do anything to screw up the use of an OBI, it's gold.