I just now performed this test: With a Google Voice number provisioned on my OBi 202, I called that number from an unrelated mobile phone number. I answered the call on the OBi-attached phone, and verified that the call was working. I then called the same GV number from a different unrelated mobile phone number. The OBi-attached phone got the call-waiting beep. I pushed the flash key on that phone. It put call #1 on hold, and it answered call #2. I could then click the flash key repeatedly, to alternate between the two calls.
So, if that is your definition of call waiting, then yes, it works. No, there is absolutely no OBi hardware problem that would cause it to not work. It should work with all OBi 2xx series devices.
Given your various issues with Google Voice, I'm going to (again) suggest that you port your Google Voice number out to a VoIP ITSP that is more of a plain vanilla telephone service, with the typical calling features they provide.