Unlocking Iphone 4 on Vodafone AU?

i have an iphone 4 on a plan with vodafone and am wanting to sell it and get a new phone. i figure i will probably get more for it once its unlocked and also widens the group of buyers.
i found steps on how to do this on the vodafone website but dont really understand how it will work.
it pretty much said to update and restore with a backup then reset to factory settings. how does this unlock an iphone?
bit worried about trying anything im not sure on as i bricked my last iphone when trying to jailbreak it (which i now know how to do)

If you are not very sure about an unlocking method then my advice is not to try it.If anything goes wrong it may result in bricking the phone and the phone will become unusable.There are legit unlock service providers like Classicunlocking.com through which you can avail a permanent unlock solution.They follow the remote unlock method.They also provide free unlock instructions and hence it will be very easy to unlock your iPhone 4.