There are plenty of other methods you can try without spending a dime. I also got mine unlocked few weeks ago. I got a working iPhone unlock software from http://bit.ly/12pfr9y and it identified and unlocked my iPhone in less than a minute. I am a happy guy now because I got it done for absolutely free.
To unlock iPhone 4, back up your iPhone and erase the contents of your phone. From there, you can go ahead and swap the old SIM card with the one for the new carrier. After completing the process, you can restore your backup.