I used these guys to unlock my Galaxy S4. I contacted them beforehand because my phone is rooted AND running a custom ROM. Wasn't sure if their service worked in this scenario. It did, perfectly, and the pre-sale support was excellent too. Got the code in less than 24 hours, punched it in and unlocked. On top of it all, they were less expensive than their competition. Can't go wrong.
Will definitely use them again with future phones and recommend them to others.