1800 numbers in any country are issued for incoming calls originating within the borders of that specific country. 1800 number owners have the option to allow incoming calls coming from abroad. So, to call a US 1800 number from Australia try dialing: 0011 1800 and so on. Note that, in case it works your call will not be free. If it does not work try using 880 instead of 800: 0011 1880 ….