It appears that many who had jailbroked or unlocked their iPhone 3G[S] did not know what they are doing or had not ask the friend who knows, like myself, before upgrading their iPhone to version 3.1 of the firmware.
It is very important that BEFORE anyone upgrade they save a copy of their unique iBEC and iBSS files before the perform the 3.1 upgrade. Failing to do so will, at the moment, made the iPhone no longer unlockable or jailbreakable. These files will also not be obtainable afterwards.
I will not go through the instructions here, instead a very detailed and easy to follow steps are documented at HackThePhone.com for the iPhone 3GS. If you own other models you can locate respective instructions there.
The bottom line is that hacking the iPhone is a technical procedure, reserved for people who knows what they are doing and should NOT be attempted by users who are not.