Is your OBi phone led showing red/orange color, or offline and can't call? Dial the Echo Test (**9 222 222 222), is this good? Dial ***1 to make sure you hear the IP Address.
Be sure to check all the connections too: OBi phone to router (and to modem) and no other devices such as extender, or switch. Your Google Voice account is probably still "Connected" but your OBi phone is not online.
Report back and let us know.
Good luck!