you are confusing jailbreak and unlocking.
jailbreaking allows for cydia to be installed which is an appstore that lets you do things that apps in the app store won't let you do (background apps, skinning the phone, tethering ect.)
unlocking allows you to use the phone on carriers other than at&t (in america).
jailbreaking is software only and will always be possible. unlocking was done with a program called yellowsnow and that whole was blocked with an update from apple. however the deve team developed ultrasnow which found another security hole, so you will still currently be able to unlock and jailbreak anything running 3.0