To do this you will need an Hexadecimal editor and have root access to your phone.
1. Make a full backup of the /efs folder
2. Get the nv_data.bin file located in /efs
3. Open it with an hexa editor (I used WinHex)
4. Go to line 181460 and modify from 01 00 00 00 00 to 00 00 00 00 00
5. Copy the modified nv_data.bin file into /efs
6. Set the appropiate owner user and group doing chown 1001.1001 nv_data.bin
7. Remove the nv_data.bin.md5 file
8. Reboot your phone
# cd /efs
# cp /sdcard/nv_data.bin /efs/nv_data.bin
# rm nv_data.bin.md5
# chown 1001.1001 nv_data.bin
To check it you can do *#7465625# and verify that Network Lock is [OFF]
I hope it can be useful for you.