If you roam, the GSM convention is that you dial local numbers as though they were international in format. So you would add +61 for Australia and discard any initial 0s if the country uses them.
In some cases you can get away with dialling local numbers in the local format. I have managed that in France but (AFAIK) it is not supposed to work.
In case this what you mean - the UK country code is +44.
Superuser 2016/17 Use Kudos to say thanks Mark answer as "helpful" only when the problem is solved Please don't send me private messages unless I ask you to. I do not work for VM. The advice I give is based on my best understanding of VM policy and practice. You rely on it at your own risk.