Press up for the phone to pop up, then press up again and type in cheat ( Numbers )
Here are some cheats: Full health and armor
Dial "3625550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "DOC-555-0100". This code prevents the "Cleaned The Mean Streets", "Finish Him", "One Man Army", and "Walk Free" achievements from being earned.
Full health, armor, and ammunition
Dial "4825550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "GTA-555-0100". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Weapons tier 1
Dial "4865550100" on the cell phone. This will unlock the Baseball bat, handgun, shotgun, MP5, M4, sniper rifle, RPG, and grenades. Note: This phone number translates to "GUN-555-0150". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Weapons tier 2
Dial "4865550150" on the cell phone. This will unlock the knife, Molotov cocktails, handgun, shotgun, Uzi, AK47, sniper rifle, and RPG. Note: This phone number translates to "GUN-555-0100". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Remove Niko's wanted level
Dial "2675550100" on the cell phone. Note: This phone number translates to "COP-555-0100". This code prevents the "One Man Army" and "Walk Free" achievements from being earned.
Add one star to Niko's wanted level
Dial "2675550150" on the cell phone. Note: This phone number translates to "COP-555-0150".
Spawn Annihilator police helicopter
Dial "3595550100" on the cell phone. The Annihilator is armed with rockets. Note: This phone number translates to "FLY-555-0100". This code prevents the "One Man Army" and "Walk Free" achievements from being earned.
Spawn Cognoscenti
Dial "2275550142" on the cell phone. Note: This phone number translates to "CAR-555-0142".
Spawn Comet
Dial "2275550175" on the cell phone. Note: This phone number translates to "CAR-555-0175".
Spawn FBI Buffalo
Dial "2275550100" on the cell phone. Note: This phone number translates to "CAR-555-0100".
Spawn Jetmax
Dial "9385550100" on the cell phone. Note: This phone number translates to "WET-555-0100".
Spawn NRG-900
Dial "6255550100" on the cell phone. Note: This phone number translates to "MBK-555-0100".
Spawn Sanchez
Dial "6255550150" on the cell phone. Note: This phone number translates to "MBK-555-0150".
Spawn SuperGT
Dial "2275550168" on the cell phone. Note: This phone number translates to "CAR-555-0168".
Spawn Turismo
Dial "2275550147" on the cell phone. Note: This phone number translates to "CAR-555-0147".
Change weather and brightness
Dial "4685550100" on the cell phone. Note: This phone number translates to "HOT-555-0100".
There you go that's all the cheats.
Chat with our AI personalities
Selected cheats should be entered into the phone during normal game play.
Activate Niko's cellphone, once you have chosen your number, and enter this using the directional keypad. After the cheat number is entered, a "Cheat Activated" message should be seen.
All you have to do is just bring up your phone. Dial the cheat codes into it and on the right hand corner it says cheat activated and look around and see if you can find you car or motorbike. If you want weapons or health dial the cheats and then they will just give you them.
Press up on the DPAD twice, and then enter the phone number for the corresponding cheat.