In GTA IV, you enter cheats by numbers being entered on phone

Vehicles appear out of thin air and I haven't even been sniffing any glue today!
- in-game website description

Glitches in the network, dial a number and life will change.
- in-game website description

There is a wide array of cheats available for the Grand Theft Auto games on most major platforms. Be advised, due to the nature of cheats, they are to be used at your own risk. It is advisable to keep a back-up save game, due to the risk of a cheat code having adverse effects on your save file. Also be aware that some of the cheats are irrevocable: Most of the cheats will be de-activated if you type in the cheat once more, but certain cheats are not de-activated, no matter how many times you type them in. Also, in certain GTA games, using cheats degrade the player's criminal rating.

You must note down that these gta cheats deter your gaming experience.