Unlock Optus Prepaid Apple 3G iPhone

According to Optus iPhone Prepaid term and condition, all prepaid iPhones purchased will be network locked to Optus, the only catch is the unlocking fee of AU$80 applied for in the first six months after the original date of activation, or after AU$80 of prepaid credit has been purchased.
My only concern is, does it work with other network after locking it? Anyone from Australia? Care to share your experience?
Apple iPhone 3G prepaid from Optus cost about $720 upfront and that would be a total of $800 after unlocking it, I believe iphone hardcore fans would pay $1000 just to get their hands on the brand spanking new gadget in ebay.
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