It has now been more than a week since someone from TPG helped me with my WiFi issues and I am pleased to report that since then I have not noticed any loss of WiFi. So, perhaps "Band Steering" was the culprit. As I don't have any outstanding issues with my new Home Wireless Broadband service, this is my last post on this thread (unless something comes up!) which was created to share my experience with this new offering.
To summarise: I am very happy with the speed (better speed than with my previous NBN12 plan), cheaper monthly fees, and first month free! My only concern is the loss of the landline phone service which means should I have to make long calls (even local or to 1300) I would now have to pay by the minute using mobile service.
