Unlike older PS2 games, SOCOM on the PSP does not have a traditional "button code" system (like Up, Up, Down, Down). Instead, cheats are unlocked either through gameplay progression or by using a third-party cheat device (such as CWCheat or NitePR) if you are playing on a modded PSP or emulator.
Terrorist Models: Completing 50 Custom Missions also allows you to select a terrorist character model in Competitive play. Legacy Support: Crosstalk
The cheats and codes provided in this post are for educational purposes only. The use of cheats and codes may void your game warranty and may result in game instability or corruption. Use at your own risk.
Let me know which direction you’d like to go (legitimate unlocks, or technical info on custom firmware risks), and I’ll help accordingly.