This blog post is more of a bookmark for me. Also, this will help you to unlock your AT&T Lumia devices without inserting SIM. I am not sure about other AT&T handsets, but it works on Lumia devices smoothly without any issues.
It’s not as easy to get a micro SIM or a mini SIM in all over the world and thus unlocking a device is quite difficult. This small post will help you to unlock the device in case you don’t have the SIM.