Thanks. I did submit a request before calling AT&T. Below is what I got. I just wanted to try some official way to unlock my iPhone. Given that AT&T provide that service, I think that's the right of a customer.

Request number: 391xxxx

Thank you for contacting AT&T Customer Care about unlocking your AT&T Mobile device. We are unable to process your request through this channel.

To submit a request to unlock your business AT&T Mobile device, please call Business Customer Care at 800-331-0500.

To submit a request to unlock your prepaid AT&T Mobile device, please call AT&T Customer Care at 800-901-9878.