I had exactly the same problem this week starting about 6 days back. Same modem VR1600v, same symptoms. I had three calls to Tech help and they more or less implied that I had caused the fault by turning my Modem/Router off/on at night or when the line droped out but I have been doing this for the last 5 years every night and every time the service drops out and the phone has never stopped working before.
I have seen multiple people on here have the same symptoms. I think their message about registering the router is nonsense. Their routers (TP-LINK VR1600) have been configured by them to set the VOIP phone settings up automatically when you power them on. You just need to plug them in and turn them on. Even if you reset the router factory settings it will still power up, download the rest of its config from TPG and then the Internet and phone will come up automatically.
The only thing I did to get mine to start working again was to keep resetting the router (Black button on the back) and I also cleaned the cable ends (The tiny gold coloured strips) going from the router to the handset with Alchohol. But the cleaning was just to rule that out as an issue, as it did not suddenly start working after cleaning. Remember that the phone cable has to plug into PHONE1 on the router which is the one closest to the power button at the back next to the power plug.
I really think the router was not being supplied the correct config from TPG and they eventually did something to get that to download and work again. I suspect that this is a known issue but they don't have the resources to fix it properly and admitting that would mean that they should give you a credit for the time that your phone service was unavailable.
This of course is only my opinion though and I have no intention to defame or damage the reputation of TPG or any of its subsidiaries.
