I think I'm a "normal" person, although some would disagree. You would have known, if you were actually using the service for its intended purpose of making and receiving actual telephone calls, and you would have run into this problem.
I support Google Voice over on their forum, and I have contacts within the Google Voice staff, so that's the source of my information (not guessing).
You can get a really inexpensive phone number from
voip.ms, and the OBiTALK dashboard has a pre-configured template to set up the number on one of the device's SPx slots. You simply click on the SP you want to configure, decline the offer to set up Google Voice on it, and go to the next page, which shows other service providers. Scroll down to the bottom of the page, and click "OBiTALK compatible service providers". The next page is a list, from which you can pick to configure service.