Hi @winstonshaw, it is actually the other way around. The Huawei modem has to be connected first then the D-link modem after.
The Huawei modem needs to be the authenticating device for the VoIP service to work.
Welcome to TPG Community!
We have located the account using your community details.
You can opt to use your own NBN compatible modem router, but please be advised that the VoIP service will not work as the VOIP service is only configured on the TPG supplied modem.
Let us know should you have further queries. Thank you.