Has anyone had problems with their VOIP phone since using the HG850a as the 'router' ?

It used to work for me until quite recently I found out that the VOIP phone no longer works. When you pick up the phone, it's got an indefinite beeping sound.

Then I rechecked the settings on the HG850a seems the VOIP settings have been wiped off. And whatever username/password pair or settings I use now doesn't seem to work. Obviously calling the Maxis center is pointless - tried it but they wouldn't disclose much information.

Any help would be much appreciated.