I have been using Home Hub 2 more or less successfully for a number of years. After a brief period with Home Hub 3 (abandonned because Port Fowarding and Dynamic DNS didn't work properly, I reverted to HH2 which worked very well with the exception that BT Fon was inactive and wouldn't allow itself to be activated. This was not a major problem as I could set my smartphone up on my home network.
However on Tuesday 3/9/13, I found I was unable to access the internet and then I couldn't access the HH2. Note I use a fixed IP address for my laptop wifi access.
After making a wired connection and setting up as DHCP client, I found much to my amazement, HH2 had reverted to its default settings (IP address, wifi security etc) with the exception of the SSID which remained as my own setup.
What is more, BT Fon was now activated - note I have done a complete reset in the past to see if I could activate BT Fon but to no avail.
This is a complete mystery and I even wondered whether BT had performed a firmware update but the last update was somewhile ago.