Just a quick FYI - I am sure I am doing this wrong, however it took me ages to figure out so perhaps will be useful for others.
I was able to connect to a VoIP service with Internode Aus using these Wiki instructions http://wiki.linuxmce.org/index.php/How_to_properly_add_support_for_SIP_providers
However I couldn't make any outbound calls until I removed the existing Outgoing Dial Rules
in the Trunks section Advanced => Configuration => Phone Setup).
It had a bunch of codes that appeared to be US related (I changed the International Settings in General Settings - this didn't appear to do anything).
I now simply have XXXXXXXXXX in the dial rules - this allows me to dial standard 10 digit numbers.
I expect I will need to update this to be able to make international calls, but for now - this is all I need.
Not sure this is the right thing to do so have not noted in the Wiki...