Hi John:
Please try making and receiving calls via your Google Voice web page, having GV call you on a real forwarding telephone number. Also, try using Google Hangouts to make and receive calls. If either of those methods fail, please post your issue over on the Google Voice help forum. If both those methods work, then you may have an OBi or home network issue, but if either non-OBi method fails, it's a GV issue.
There is an isolated issue right now being worked on by Google Engineering involving a CODEC mismatch between two carriers, that can cause this symptom, so it's necessary to rule that out before wasting time diagnosing an OBi-specific issue.