There are no tap in cheats for this game... But SuperCheats.com does have an exclusive browsable guide for the complete game here. As well as a complete walkthrough there are also seperate pages just for antenna and emission locations, plus a seperate player response page.
Unlock First Person Shooter (FPS) Mode: After you have completed the game you will have unlocked the FPS mode, it also gives you infinite ammo in that mode as well. Just select the FPS mode on any mission.
Unlock Bonus Weapons and Items Complete missions to unlock extra weapons and items for use in the game. Below is a list of what becomes unlocked when a certain mission has been completed.