i too got an omnia and wanted to get into geocacheing with it, then i learned of the gps issue
there may be hope
there is a rumor around that a firmware update will allow the gps to work on the omnia
release date per the rumor is may 11th
there are also custom roms available that unlock the gps, but use at your own risk as they may violate your warranty and brick your phone
google will direct you to the locations