Telstra is good

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alright, first of all do you have any idea as of how old the iPhone is?
depending on when it was
made, the iPhone bootloader differs, and depending on what version bootloader you have, will depend on if you can unlock your iPhone with software, (so for now we wont worry about the turbo sim).
goto this site, and follow the tutorial,
iClarified - iPhone - How to Check Your iPhone Bootloader Version (Windows) On this site you will find out what version bootloader you have.
This is important, as at the moment only bootloader 5.8 is able to have the baseband downgraded for unlock with yellowsn0w.
so, what bootloader do you have? 5.8?
Continue
To unlock your iPhone, you need to downgrade your Baseband, from 2.30 to 2.28 for iPhone 3Gs, but to do this you need the 5.8 bootloader (i gave you the link to guide you on how to find what version bootloader you have)
If your
bootloader is version 5.8, then goto this site,
iClarified - iPhone - How to Downgrade Your iPhone 3G 2.30 (2.2.1) Baseband for Unlock which will guide you on how you can downgrade your iPhone Baseband so you can unlock it.
Sorry about all this, haha it must be the most confusing post ever, but it is a lot of info to take in. I was unsure of y the turbo sim was not working, therefore i figured if you could unlock your iPhone by using the official 3G unlock yellowsn0w, it would be heaps easier.