International texting is a great way to communicate to a person overseas! May I ask is the number that you are texting in Australia a Verizon Wireless number, another US mobile number, or a native Australian mobile number? To be on the safe side, I have noted the dialing pattern below for all three situations.
For example, to text an Australian number simply dial 011619876543210. Hopefully, my example didn't confuse you. If it did then here's a link that will explain it as little better.
If you have any additional questions then feel free to reply to this message for assistance.
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