Obii is still working, and they sent out an email saying Google pushed off the date a bit, but that it will likely stop working "soon."
But again, that has nothing to do with OP's initial question of whether overseas affects use, and the answer is that it does not. When logged into Gmail, I can call no problem using Google Voice (not Hangouts) to any US/Canadian number, for free, regardless of where I am in the world, with no proxy/VPN needed