The first configuration screen is "System".
Ensure you remove DHCP, and set the ATA to use a Static IP, as in the below screen shot.
Next, choose "Regional" Ensure all the Call Progress Tones are set as below, this is the correct settings to make the ATA behave like the Australian PSTN network would.
At the bottom of "Regional", there are further settings to adjust. The FXS Port Impedance should be adjusted to 220+820||115nF.
You can adjust the input gain as required, this will make either inbound or outbound audio 'less echo' or 'louder' depending on the desired requirement. DTMF playback is important if you make calls to 13X numbers (or "Push 1" type menu systems).
Next, choose "SIP"
Check the RTP Ports are set in the desired range. If you are having poor audio quality, reduce the RTP packet size by 0.01.
Next, choose "Line" Ensure the Jitter level is adjusted as appropriate, Extremely high will make the ATA behave better in environments of traffic where the latency may 'increase' and 'decrease' rapidly (commonly a cause of audio breakup).
The Proxy settings and Subscriber Information should be adjusted as appropriate. The details there will of course, not work.
Scroll to the bottom of Line. Ensure the Preferred Codec is set to G729a, but do not set Pref. Codec Only to "Yes". DTMF settings may require tweaking depending on your handset, and it's interaction with menu systems.
The dial plan included is 'basic'. This dial plan will allow all numbers to be sent to the VoIP system, and as such this setting requires numbers to be dialled in full digit form (with area code as well). There are other dial plans that you can enter to restrict calls to certain areas, and give the ability to dial 'local' type numbers without area code. Ensure FXS Port Polarity is configured correctly.