Hi:
You're right; it's a risky solution, as you've already found. If your panel is professionally monitored, I strongly recommend converting to a direct IP connection with a 4G LTE backup communicator. That's what ADT uses now, for example.
As for your OBi, if you're attempting to use this with Google Voice, then go to the OBiTALK dashboard, click on the Google Voice SP, and check-mark the box to indicate that it is being used with an alarm system. Note that this typically cripples the ability to use touch-tone entry on calls you place, so it's best to use that SP as a dedicated line for the alarm.