SingTel, the parent company of Optus announced in a press release that they will be selling the iPhone in the Australian market:

SingTel, Bharti Airtel, Globe and Optus today announced that they have signed an agreement with Apple to bring the iPhone to Singapore, India, the Philippines and Australia later this year.

This confirms the rumors from earlier this month, and, more importantly, confirms that there is no exclusivity arrangement (in Australia at least) like that with AT&T in America.