I am not sure if this will void the warranty on the phone, so try it @ your own risk.

Samsung Omnia
This method was developed by _TB_TB_ from xda-developers.com and will work only for Samsung i780 and Samsung Omnia ( i900 )
- Download lock.zip
- copy all three .lnk files to your PPC
- run Lock.lnk
- enter valid MCC/MNC of any carrier (I used my “real” SIMLock carrier ID, list: http://en.wikipedia.org/wiki/Mobile_Network_Code ; eg. 26001 for Poland, Plus)
- As NCK, enter an unlock code , for eg : 12345678
- tap OK (it should tell that SIMLock enabled)
- run Status.lnk to see if its locked
- run Unlock.lnk
- enter code entered in point 5 (12345678)
congrats you have just SIM unlocked your device for FREE !!!
Alternative method, works on i780, no copying of anything required:
- In the phone dialer app, type in *7465625*638*#
- enter valid MCC/MNC of any carrier (I used my “real” SIMLock carrier ID, list: http://en.wikipedia.org/wiki/Mobile_Network_Code ; eg. 26001 for Poland, Plus)
- As NCK, enter an unlock code , for eg : 12345678
- tap OK (it should tell that SIMLock enabled)
- in the Phone dialer, type in: *#7465625# to check if you are locked.
- Finally, to unlock your phone, type #7465625*638*# in your dialer and enter code entered in point 3 (12345678)
Update on 06th Jan 09 – another way to get the Samsung Omnia unlocked
Go to the registry, HKCU\System\State\PHONE, and wrote down the first 6 digits of the value of the IMSI entry.
- type *7465625*638*# to set
- type the first 6 digits of the value of the IMSI entry here.
- type your new NCK (12345678), then OK
- type *#7465625# to check your lock (network lock still enabled)
- type #7465625*638*# and type your NCK (12345678)