I'm not sure what you mean by letters, but you can activate cheats by going to your cell phone in the menu and calling numbers like #909.
Here's a list of Saint's Row 2 cheats for the PC, I'm pretty sure they're the same for Xbox 360.
http://www.cheatcc.com/PC/saintsrow2cheatscodes.HTML
either search the cheats for xbox 360 or white is RB and black is LB.
in grand theft auto
X,L1,SQUARE, R1, O, DOWN, UP cheat codes exist in grand theft auto!
go to cccheat
that's a mod.
Cars
shift i
go to gtasanan.com
Hello
in the phone
no that's a dumb question
type in your keyboard all missions done in grand theft auto 12345678910
Yes