How can I unlock my Samsung Galaxy Ace? I have just purchased a Galaxy Ace locked to a specific carrier. I was wondering if it is possible to unlock the phone for free without having to pay for it?
Yes, as with many of the Galaxy devices it appears that the unlock code is actually stored on the device and easily accessible (as long as you have root access).

This XDA post should guide you through it.  Note of course that it might not work and you could brick your device by rooting, in addition to voiding the warranty.  In my experience the Galaxy devices are hard to brick and unlikely to be problematic.