Read
this for the original breakdown.. But the tips to unlock your Omnia are as follows:
Go to the registry, HKCU\System\State\PHONE, and wrote down the first 6 digits of the value of the IMSI entry.
1. type *7465625*638*# to set
2. type the first 6 digits of the value of the IMSI entry here.
3. type your new NCK (12345678), then OK
3. type *#7465625# to check your lock (network lock still enabled)
4. type #7465625*638*# and type your NCK (12345678)
5. enjoy.
This is a GSM hack...
Here is the original thread from XDA...