While playing, (quickly) press Right, X, Right, Left, Right, R1, Right, Left, X, Triangle for five minutes of invincibility. You can also dial "Painkiller", which is numerically spelled "1-999-724-6545537" on your cell phone. After five minutes you have to re-enter the code.
Full Weapons & Armor
While playing, (quickly) press Circle, L1, Triangle, R2, X, Square, Circle, Right, Square, L1(3). You can also just call "1-999-887-853" (TURTLE) on your cell phone.