If you want a permanent unlock that doesn't require typing a code every time you launch the game, you can modify the game's internal files.
Now, you can select any mission from the mission select screen. project igi 1 all missions unlock top
The most reliable way to unlock everything instantly is by using the built-in developer cheat code. This works on almost all versions of the game, including the GOG and Steam (via wrappers) versions. Stay on the Main Menu screen. If you want a permanent unlock that doesn't