I have recently bought an Australian sim card (Telstra) for my iphone 4. It works fine with ANY phone that is within Australia, but when I want to text or call someone abroad, it only works if that person does NOT have an iphone! I have checked this thoroughly so I am absolutely sure that is the case...
Been to the Telstra shop, sim card is fine, spent a lovely 45 minutes on phone with a guy from Apple tech support but even they had never heard about anything like that.
Could anyone help? I have reset everything, my software is up-to-date... What else could I do/check?
Cheers