I've used cellunlocker.net twice in the last couple of years, both times to unlock my own phone after my original contract was up (a Blackberry and a Samsung Galaxy). Yes, your provider will do that for you, but Cell Unlocker is less expensive. They are responsive and accurate. The first time I had a minor issue, and their tech support was responsive and written by a real person, and fixed it for me. The second time, nothing more to do... worked 100% first try.
I would use them anytime.