For those of us without broadband (that's you Mum and Dad) my boss has recommended www.jajah.com
Apparently if you all sign up you can make free calls between Australia and the UK via the landline, as opposed to Skype which uses the internet. Both people have to be members, and then you hop online, select who you want to call and it calls your phone. You get a 150 minutes a week, 500 minutes a month apparently. So yeah, it's completely free, and via landline. Should save everyone some money.
If you sign up let me know. I've just signed us up with the username "damienmason"