Just wanted to add that I am having the same problem. Out-going is fine, but in-coming just flat out would not ring, and eventually went to the GV voice mail. When I tried to call in (using my own cell phone) to my "home/Obi/GV" phone, it connects, but the phone didn't ring and went I tried to pick it up, it was just a ring tone.
I don't think I've changed anything and it seems like it could be a system problem, but not a local (my) problem?