Telstra has announced they will no longer charge a fee for unlocking your iPhone.
Currently, when you purchase a new iPhone from Telstra it is locked to the Next G network by default, and will only work with a Telstra SIM card. Telstra used to charge $100 to unlock the handset so that it could be used on competing carrier's networks. Now they won't charge anything, although the handsets are still locked by default.
In order to unlock your iPhone, simply call Telstra on 1800 iPhone (1800 474 663). Make sure you have the following details: your mobile number, your iPhone serial number and your iPhone IMEI number. You can locate these by pressing the Settings app, scroll down and select General then press the About tab.
To complete the unlock process you need to have the newest version of iTunes installed on your computer. Once the unlocking has been processed, the next time you tether your iPhone to your computer, iTunes will unlock the phone.