Apple retailers frequently discount iPhones, Macs and iPads for Black Friday.
Optus Announces iPhone 3G Pricing in Australia
The pre-paid price for the iPhone is $729 (8GB) and $849 (16GB) and allows you to sign up as needed without need for a long term contract. Pricing appears to start at $30 per "recharge" but without data service. 50MB is included in the $40 Turbo Cap pricing. Full details are available at Optus.
The post-paid pricing appears slightly more confusing (to this U.S. resident), with no upfront phone charge, but a monthly "handset repayment" which ranges from $0/month to $59/month depending on the plan and model of iPhone you get.
"Cap" plans start at $19/month with 100MB of internet data and "$50 of calls and text". Prices go up from there, with the highest price priced at $179/month with 1GB of data and "$1500 of calls and text". Full details are available at Optus.
Vodafone and Telstra are also providing iPhone service in Australia but have not yet announced their pricing plans.
Update: Telstra announced their plans today:
iPhone 3G will be available from Telstra on July 11 with a range of specially designed Next G iPhone 3G plans that meet the needs of any customer. The Next G iPhone 3G plans start at $30 per month with an upfront cost of $279 for the 8GB model and $399 for the 16GB model. Customers will receive the 8GB iPhone 3G model at no cost with the $80 plan and either the 8GB or the 16GB model at no cost with plans starting at $100 per month. All plans include free Wi-Fi access at Telstra hotspots and require a 24-month contract.