How to network unlock my AT&T Samsung SGH-i957

I have a Samsung SGH-I957 which is lock to at&t , i have rooted it, installed busybox, tried to unlock it by editing the nv_data.bin file but as bad as it got there was no nv_data.bin file located in the efs just redata.bin and some others.

I am very confuse on the way forward.

more details:

Android 3.2
4G LTE