Don't post the same question in multiple places.
There are two different ways to "call" somebody using Hangouts. You can have a direct Hangouts<-->Hangouts chat, which does not use the telephone network, or you can use Hangouts to call a telephone number (that may or may not be a Google Voice number, or just some regular telephone number).
OBi devices are not Hangouts clients. You cannot make a Hangouts-to-Hangouts chat to an OBi; you need to dial a telephone number. If that number happens to be assigned to a Google Voice account that is set up on an OBi, the OBi-attached telephone will ring, just like any othe telephone call.
Make sure you are using the "call phone" function in Hangouts -- the little telephone handset icon. Try calling some other telephone number, like a cell phone, and see what happens. Does it work? What, exactly, happens when you call the GV number assigned to the OBi? What do you hear on Hangouts, as the person making the call? Does it ring, or do you get an error, or what?
Note that, when the Hangouts client is logged into a Gmail account that does not have its own Google Voice telephone number assigned, the caller ID you are sending to the other party will be "unknown". If you are blocking anonymous callers on the receiving end, you won't receive the call.