To unlock SGH-I777 with GINGERBREAD 2.3.6 or 4.0.4 you have to downgrade it to GINGERBREAD 2.3.4 first
Download firmware http://www.UnlockClient.co/i777.zip and extract it to the root of your harddrive disk C:/i777
Turn off your phone, then press "Volume down" button and press power shortly (keep pressing "volume down")
until warning message will appear.
Release "volume down" button. Now press "volume up" to continue. Android logo should appear.
Connect your phone to computer with USB cable and wait until drivers are installed
Launch Odin3 v1.82.exe loader file.
You should see yellow ID:COM number
Click PDA button and open I777UCKH7-REV02-home-low-CL503881.tar.md5 file
Check "Auto reboot" and "F.Reset Time" checkboxes
Dont check "Re-Partition" , "Flash Lock", "Phone EFS Clear", "Phone Bootloader Update" checkboxes
Press start and wait until uploading is complete.
Its not necessary, but as suggestion you should do the hard reset by dilaing *2767*3855# after downgrading and
it will wipe out all user data.