I also have a Google Voice account, do not have GooglePlus, and use Ooma basic for my home landline. (Not comcast).
I haven't used GV in quite a while, but I just tried going to the web site on my PC, and initiating a call, and it worked fine.
I'm finding I can't dial out from my desktop computer with GV. I can receive and I can text but I can't voice call.
What exactly happens when you try?