Hello Richard. If your AT&T iPhone has Outstanding Financial Balance, then it is not blacklisted. However, there are a few unique cases that a device can get blacklisted due to financial issues. If your device is indeed blacklisted (inside AT&T's blacklist database), then it cannot get unlocked. If it has an outstanding financial balance, then there are a few services that can unlock it. You can send us a full IMEI report to evaluate it and propose you a solution.