Have done some research and found a forum on Whirlpool which tackles the problem with various brands of routers including Billion and Netgear. Mine is a TPLink AC1750 and what they suggest worked. I use iinet as my VoIP service provider.
Here is the link to the Whirlpool discussion but have also included what I actually did.
http://forums.whirlpool.net.au/archive/2236481
When using the quick set-up it was the sip.wa.iinet.net.au that was required along with the phone number and password to receive calls.
To make calls I had to do all of the following:
- ON YOUR ROUTER disable the SIP ALG setting.
- ON THE SPA112 set the following to 'YES' - 'NAT Mapping Enable' and 'NAT Keep Alive Enable'
- ON THE SPA112 make sure the Proxy and Outbound Proxy are set properly. for me it was iinetphone.iinet,net,au for the Proxy and sip.wa.iinet.net.au for the Outbound Proxy.
That's it.
Works great although there is a long delay between dialing and the call going through but that's okay. It works.
Hope this helps.