As of now, there are no software sollution to unlock any 3G iPhone except those thats not locked to any particular telcos i.e NZ iPhones. There is hardware sollution that uses a sim adapter to trick the phone in seeing its a legit sim card like TurboSim.

Never ... since the 1st gen iPhone.

Contract and lock phones are two different things.

U can have a contract phones with subsidy (cheaper phone) or u can buy a non contract phone without subsidy (higher price).'

Both are still locked to AT&T network.

Locked 3G phone can only be jailbroken and can't unlock at the moment. If its as easy as reflashing with a pwned firmware, won't the dev team done it already? Right now the problem is with the new bootloader chip on the commboard. Its different from the 1st gen phone and the hack they use on the first one is not working on 3G phone. Right now they are making progress and only time will tell when the unlock for iPhone 3G will arrive, something like the 1.1.2 unlock last time if you all remember. It takes around 2 months for them to crack that thing.

How sure are you that singapore iPhone not going to be locked?