There are too many threads about this. iPhone 4 is not unlockable unless on baseband 1.59.00. I'm going to blatantly assume that you don't have it.
The only other way your iPhone is getting unlocked is via a carrier unlock or the gevey SIM. For the carrier unlock, your baseband doesn't matter, but a lot of carriers won't do it (AT&T, Telus, Rogers, Bell). However, if you're located in the UK, I believe that both Orange and O2 will unlock your phone for a mere 15 euros. In addition, I am not quite sure what the requirements are to use the Gevey SIM.