Changing the Sigma unlocking mode
Make sure your operator's sim card pin code is activated first.

Turn on your phone.   The phone will ask you to enter your pin code for your operator’s SIM card.  Enter your PIN CODE followed by UNLOCK CODE MODE.  Eg. 12340002. Listed below are unlocking codes.

UNLOCK CODE MODES:
0000 = No read will be altered (SIGMA is basically deactivated in this mode)
0001 = The first read will be replaced (Most Nokia, Samsung, Motorola...)
0002 = The second read will be replaced (Few Nokia models, especially N Series)
0003 = The first two reads will be replaced
0004 = The third read will be replaced
8185 = For most sharp models (this is the default configuration)
8191 = TMSI mode (patch all imsi reads)