Many thanks to yjwong, ywkwy and the other many people who have contributed to this thread. Just dropping in to say that I managed to use the HG850a to handle VOIP with the guide that was posted.

It has been for the longest time that I wanted to replace the Maxis default modem with something better. Glad I found time today.

So far so good. Will give feedback on stability. Cheers.

Been awhile since I last check in here. Initially I had no problems with the VOIP after ditching the Thomson and connecting it directly to the HG850a. It was until late last year that I suddenly had no access VOIP. Thought it was a problem on Maxis side but they reported nothing. But I swear they changed something to make it not working. And the post above probably confirms it. Was too lazy to bring out the ladder and connect the laptop to reconfigure the HG850a again since it's located on a server rack high up.

So to put the long story short, I got a Cisco SPA122 ATA to handle the VOIP connection. Plugged into my switch and so far after working out some configuration hitches with a kind soul, no problems now.

Yes, new model is Cisco. Originally it was Linksys. That's the hardware issued when you subscribe to some 3rd party SIP accounts.

I got it shipped from US. I tried to find one locally but to no avail. Nobody seems to know what it is. Perhaps you'll be lucky. If not, let me know. If I buy something else from US, you can tumpang me to buy the SPA122.