Como en varios casos la Box da las instrucciones
UNLOCK INSTRUCTIONS:
Micro-USB cable:
1. Phone must be powered on.
2. Type *#0808# and select 'DM+MODEM+ADB'.
Operation: Unlock
Selected model: SGH-I537
Selected port: COM50 SAMSUNG Mobile USB Serial Port
Software version: 29.5
Reading phone info...
Reading IMEI... OK
IMEI: 357365054288069
Unlocking... OK
Reseting... OK
Unlock done
Done with Samsung Tool PRO v.29.5