It may have been overtaken by more recent technology, but in the (nearly) 7 years we've been here, I've always used a phone card to call back to the UK from a landline. Used to use it from a payphone before we had our own landline. I get mine from Aussie Phone cards (will find a link in a minute) and you call a local number, enter a pin code (or have it 'mapped' to your landline if you always use the same one to call from) and then get thousands of minutes chat for about $30.
My parents are on a scheme in the UK where they get free international calls at weekend - so might be worth suggesting that for those rellies you'e leaving behind too.
Think this is the starting point for buying your initial phone card - you can do it online and top up online as well so could probably do from the UK: Australia Phone Cards- Find the Cheapest Phonecards in Australia
The one we use is about 1.5c per minute to a UK landline - so 2000 minutes of chat for $30.