Cheat: Unlock All Missions:
Pause the game during the Cuban Operation, while playing as a support troop. While paused, enter R1, R1, R1, R1, X, CIRCLE, L1 + L2
Cheat: Enable Online Voice Chat:
To enable voice chat during online gameplay, the following cheat must be entered on the "Press Start Button" screen by the host: R1, R1, L1, L1, R1, L1
Other players can have the cheat enabled, but it is only necessary for the host to have it. If the host does not have the cheat enabled, no one will be able to use the voice com during gameplay.
Source? Here it is.