To send a TXT to an international mobile number you'll need to enter the mobile number in international format.
Example
If the mobile number you want to send a TXT to is 123123123, you would enter the number as:
+[country code]123123123.
"+" is equivalent to the international exit code.
Click here to view which countries you can send a TXT message to.
TXT sent overseas from within Australia are charged according to the terms of your Contract or Prepaid Plan (160 characters or less).