The unlock code for the Opto 456 and 535 boards allows a user with appropriate software to enter the password, and then can tune in the cellular band using the Opto board. This allows the board to be tuned to the frequencies used by cellular telephones. You should know that monitoring cellular telephones has been illegal under Federal law since 1989.
Many states also have laws making it illegal.
Opto has been shipping a newer version of the OS535 board since early 1997 that will not accept this code for unlocking frequency coverage. They still sell full coverage boards for export and authorized US users. More than one monitor has reported intercepting an agency with trunked 800 MHz radios, using simplex talk around on their Ht.'s for sensitive comm. Listen for comm. I continue to hear this in Alameda County.