OK, so Obivoice support indicates they simply do not have a carrier that can complete calls to these areas. I guess that would explain it. I wonder how many exchanges are out there to which they can't terminate calls?
Funny how one assumes the phone network would (or should) work universally, at least within the US. It's going to get interesting in light of the ruling. It would be like the post office dropping mail delivery to certain zip codes.
What's troubling is that some carriers WILL terminate the occasional landline-quality call just fine. Then the next six times will take 30 seconds to complete, or give you an endless Euro-style ringback with no answer, or have one-way audio, or suffer from extreme compression and delay. Voip.ms is one carrier I have not tried, will give them a look--thanks.