I've finally found the perfect service for the Expat. Jaxtr is a service which makes international calls easier, cheaper and much more convenient. It basically means that I can now make calls to the UK from my Australian mobile phone at a cheaper rate than calling from my home phone - even cheaper than using a calling card!
It works by assigning you a local number in your country that you can call, which is then switched through jaxtr's VoIP network to the destination number you have assigned overseas. So for instance, I simply go in to Jaxtr and enter my Dad's phone number in the UK, it then assigns me a local Australian number that I can use that will get forwarded to my Dad's number. Calling UK numbers from Australia using Jaxtr costs 1 jax per minute, and you can purchase 1000 jax for $10 US, so basically it costs 1c per minute. Of course you still have the cost of ringing the local Australian number, but on my Vodafone plan I get $150 worth of call for $29 so that's also really good.