The game has a fixed roster of playable characters, and you cannot unlock additional characters through codes.
However, you can acquire additional models through:
* Leveling up: As you progress through the game, you unlock certain characters by completing specific missions or reaching certain milestones.
* Downloading additional content: Some versions of the game may offer downloadable content (DLC) that includes additional models.
If you are looking for more playable characters in *Transformers: Revenge of the Fallen*, your best bet is to keep playing and unlocking them through the game's natural progression.