Devices that are under the 12-month warranty period should receive the new firmware update automatically (no user action required).
All other devices will need to be updated manually. Assuming your device is on your OBiTALK account, you can go to the OBiTALK device dashboard and click the orange triangle to perform the update. Otherwise, you can download the firmware and install it yourself via the device's local web user interface.
See:
http://www.obitalk.com/obinet/pg/obhdevDevices that haven't been upgraded will lose access to Google Voice in the next week or two.