All Weapons
     While  playing a game enter: R2, L2, UP, Down, Cross, Up, Square,
Cross.

Invincibilty
     Enter  this  code  while playing a game: R2, L2, Up, Down, Cross,
R2, L2, R1, L1.

Level Select
     At  main  menu,  enter  this  code:  R2,  L2,  Up,  Down, Square,
Triangle, Circle.

Unlock Sawed-off Shotgun
     Beat any two missions with a Silent Assassin ranking.

Unlock Silenced Ballers
     Earn a Silent Assassin ranking on any mission.

Unlock the M4
     Earn  a  Silent  Assasin  ranking on the St. Petersburg missions.
Once you complete "Invitation to a Party," you unlock the M4.