Daas: You get free US AND Canada already by using google voice as your calling card. And you get the same international rates whether you use it as a calling card or directly through an Obihai device. The benefit is being able to dump your local phone company, while getting the same service.
Personally, I think the reliability of a cellphone replaces the need for a landline. In fact, many households are already cellphone only (not even using a VoIP or google voice type setup.) Landlines are a 100+ year relic, with the technology little changed from the days of Alexander Graham Bell. And Verizon and AT&T are slowly but surely phasing out their investments in landlines letting them languish while just milking them for whatever they can without investing in upgrading or even basic maintenance in them.