Google Chat must of course be checked; you must also have made a successful call from Gmail. Please report your results from troubleshooting, as described in the other thread. In case you didn't see them:
Log into a failing OBi directly and see what shows, if anything, in Call History after a failed inbound attempt.
If nothing is logged, shut down the OBi, log into the account with Gmail and retest. If that doesn't ring, either, then this is obviously not an OBi-related issue. If Gmail rings ok, log out of Gmail and do a test with OBi connected directly to modem (or otherwise confirm that the problem is not router related).
If the call does appear in Call History, where was it routed? If not to the Phone port, check InboundCallRoute for the SPx in question. If it was sent to PH, perhaps this is a ringing voltage, waveform, frequency or cadence issue. Try answering a call when it should be ringing.