JMills87 over on our sister site, iPhoneForums.net, is currently covering some of the most exciting carrier unlock news we've had for a very long time. It appears confirmed that there is a vulnerability via SAM which will allow any iPhone 3GS, 4, or 4S running 5.x firmware to be unlocked regardless of the baseband it has provided it is jailbroken. The unlock is achieved for a specific SIM card (rather than unlocking the device) and it sounds as though this vulnerability will be patchable by Apple, so now is the time if you need an unlock!
Here is a link to the thread on the other site - Unlock any jailbroken iPhone..... REGARDLESS OF BASEBAND!