This is a very easy cheat. First go to middle park on the 2nd island.(The black area on land by the top)Then with your car run over as many people as you can and money will fly everywhere!(you might want to have a wanted down cheat because cops get on your tails!) then collect all the money and mamamia youra onea richa mana!

How you turn invisible is be at the hospital close to the police department. Get a sniper rifle out and go to the stairs of the police department. You should se a burger guy on the street. Get the scope out and look to the right and you should see a propane tank shoot it and when you get out of the scope, you will be invisible

Drive a car into the phone box but just as it is about to hit the phone box jump out of your car.

If you are driving a car really fast and want to stop but you will crash, press up so that your phone comes up and then go to the camera and your car will stop straight away. Note: you can only do this when you recieve the camera phone from Playboy x

Fly a helicopter to the statue of happiness. Jump out of the copter so you land on the highest area with doors. One of the 4 doors will have blood stains on the floor in front of it and 2 signs on either side saying 'no hidden content through here'. That 'door' is actually NOT SOLID. so walk through it to find a ladder. climb the ladder, and you will be face to face with the beating heart of the city! If you shoot it blood will come out.

An Infernus is the rarest and most expensive car in the game. Here's the cheat
243-800-6246

I don't know if this works with all boats, but if your stranded in the ocean and you see a boat called tropic then you can swim in front of it and if done just right you will take small ammount of damage and actuall end up inside of the boat!

Hope this helps when your stuck out in the ocean.

Pull out Niko's phone and dial these numbers for the corresponding effect

Raise wanted level:
267-555-0150

Remove wanted level:
267-555-0100

Restore armor:
362-555-0100

Restore health:
482-555-0100

Remove Ammo Limit:
Get 100% completion

Playboy X will give you a camera phone at some point in the game, when he does go to the nearest internet cafe and go to a ringtone website and start buying. When you log off you will see that it looks like you only spent $100 on all the ringtones.

Go to happiness island and then on trhe secon level of the statue keep walking around until you find the shirt

Sometime in the game you will get to choose to kill Dwayne or Playboy x.

If you kill Playboy x you will get his apartment and a tight black leather jacket and green cargo pants

Hey wanna get alot of money fast? Well find a Stockade hers a link for the Picture [ http://media.gtanet.com/gta4/images/vehicles/STOCKADE.jpg ] Then steal it..Take it somewere with alot of room, and throw a granade UNDER the truck..Step back and collect the money off the ground..Its tricky cause the trucks on fire -_- but it's good if you want money :D if you don't like this then just find Steves cars..thers a good reward in stor for you for every car..just take it there neat not smoldering or anything.

All you have to do is got to the Garage (where you go to bring that guy stolen cars)make sure you have either a turismo or comet code on your cell.

(recomend turismo it's worth 11,000)(comet is only 6,000)

Just keep returning them in and you will become rich in no time.

(don't know if it works if you have not beat the game)
Does for sure if you have

Weapons:486-555-0150

Health: 482-555-0100

Weapons 2: 486-555-0100

Get Rid Of Cops: 267-555-0100

Not so much of a cheat, as another GTA mystery, but for this you will need a helicopter. Get a cab and go to the heli-tours place. Steal a helitours maverick, because this isn't possible by foot. Once you get in a chopper, go straight to Happiness Island (Statue of Liberty), and fly around the Statue a bit. At this point, you will need to jump out on the highest available tier on the statue. It is just the same as the ones below, 4 doors, none of them look like they open. On one of them, it won't open, but you can walk straight through, into a room with a ladder. Go up the ladder inside the statue, to see the mysterious pumping, chained heart. P.S - You probably WILL die trying to get back down, so unless you want a picture, don't save it. P.P.S - Theres a pigeon somewhere on a lower tier at the back of the statue, you can kill it to be on your way for an additional 2.5% completion.

Bean Machine Coffee: 555-0110
Express Car Service: 555-2222
Express Car Service: 555-3333
Fire Proof Doors: 555-5700
Hero Shop: 555-8575
LCPD Recruitment: 555-RECRUIT
Liberty Construction: 555-1274-73
No Problemo Bail Bonds: 555-945-733-92
Storage: 555-221-3877
Superb Deli: 555-4674
The Serrated Edge: 1-800-555-5555
Used Auto Parts: 555-7300
Vinewood Laundromat: 555-5123

Annihilator Helicopter
-Kill all 200 Flying Rats

Rastah Color Huntley SUV
-Complete 10 Package Delivery Missions

Health And Weapons Call GTA-555-0100
Weapons Call GUN-555-0150
Advanced Weapons Call GUN-555-0100
Health Call DOC-555-0100
Wanted Level Down Call COP-555-0100
Wanted Level Up Call COP-555-0150
Climate Change Call HOT-555-0100
Spawn Cognoscenti (Mafia Car) Call CAR-555-0142
Spawn Sanchez (Dirt Bike) Call MBK-555-0150
Spawn FBI Buffalo Call CAR-555-0100
Spawn Turismo Call CAR-555-0147
Spawn NRG900 Call MBK-555-0100
Spawn Comet Call CAR-555-0175
Spawn SuperGT Call CAR-555-0168
Spawn Police Chopper Call FLY-555-0100
Spawn Jetmax(Boat) Call WET-555-0100