To call or SMS an overseas number from your mobile you will need to enter the number as shown below:

Calling Internationally From A Mobile: Dial: 0011 + [country code] [phone number]

SMS Internationally From A Mobile: Dial: + [country code] [phone number]

If you are calling or sending a message to an Australian mobile overseas and the other person has International Roaming turned on, just call or SMS their number as normal.