If you get a tone in obi phone but when you dial you get this message
“network status ip address not available”
the problem may likely be that your obi is disconnected from your router as was in my case. Somebody moved the router and the cable got loose.
You can login on http://www.obitalk.com/obinet/, after login click the status of your obi. If it is not green or has an error, proceed accordingly.