This thread is now archived and closed to new comments. Some of the links and information provided in this thread may no longer be available or relevant. If you have a question please post a new topic.
You could try a factory reset but I think you will have the same problem. The VOIP configuration settings have to be downloaded to the modem and I think this will only occur once modem is connected to your NBN service. Once the modem is configured the phone should then work when on 4 G backup.