I set up a Grandstream HT814 4 port ATA today and thought I would post the dial plan for others to copy. This dialplan inserts the area code 02 in front of all NSW/ACT numbers (starting with 4,6, 8 or 9). This could easily be modified to suit the other states.
{<=02>[23456789]xxxxxxx | 0[23478]xxxxxxxx | 13[12]xxx | 1[38]00xxxxxx | 000}
Edit: I went ahead and did the plans for the other states.
{<=07>[23456789]xxxxxxx | 0[23478]xxxxxxxx | 13[12]xxx | 1[38]00xxxxxx | 000}
{<=03>[23456789]xxxxxxx | 0[23478]xxxxxxxx | 13[12]xxx | 1[38]00xxxxxx | 000}
{<=08>[23456789]xxxxxxx | 0[23478]xxxxxxxx | 13[12]xxx | 1[38]00xxxxxx | 000}