I did explain. It's possible to continue to make outbound calls, while inbound calls will fail, if you have a XMPP client other than an OBi 200 series ATA or 10x2 IP phone, which can share the connection. This was a widely-discussed topic back in the OBi 100/110 days, where only the last client to register would receive inbound calls.
I also hinted at the other universal cause of this symptom: any Gmail account that has accepted Google's Terms of Use (by clicking a box the first time a call is placed) can make outbound calls. That account doesn't even need a Google Voice number. If the OBi is accidentally registered to the wrong Google account, then it will make calls, but not receive calls. You can check this by clicking on the SP that is assigned to Google Voice, and, on the next page, look at the Gmail address in use. Then, look at that same Gmail address' Google Voice configuration on a web browser, and see if it has the inbound number.