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.
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.
Works great although there is a long delay between dialing and the call going through but that's okay. It works.
Network Address Translation (NAT) Settings for Lines on PAP2T and SPA3102 Phone Adapters
The objective of this document is to configure Network Address Translation (NAT) settings for the lines of communication on the PAP2T ...
Speed Dial Settings on SPA100 Series
Speed Dial Buttons are often used to make the process of calling regularly used contacts quicker and with one button. This option is used in place of dialing the entire phone number in. ...
Firmware Upgrade on SPA112 and SPA122
To upgrade the firmware a specific file must be downloaded from the Internet and uploaded to the device. Upgrading your devices can be very useful. Firmware upgrades can fix software bu...