I must have gotten 5 invites from Ron Workmeng last night to play multi player GTA IV and every time I accepted the invite it would tell me I was unable to join the game and it was taking me back to single player. While I did get a little frustrated with the whole situation it was quite easy to release that frustration in the form of nuking a bunch of cops just doing their jobs. Also it helps if you go into the burger joint and just start blasting people because they only have one item on the dollar menu. Also here are the cheats I was able to find on the net incase someone has not posted them yet, but it is far more likely that someone did post them and I just did not see them.


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Cheat mode
While playing the game, press Up to display Niko's cellphone. Press Up again to access the keypad. Then, enter one of the following codes to activate the corresponding cheat function. Once a code has been entered correctly, a new "Cheats" menu option will be available on your phone, below "Options", where you can access the cheats without having to enter the phone number again. Note: Do not save the game after enabling a code to avoid unforeseen problems. Enabling some cheats may prevent achievements from being earned.

Full health
Dial "3625550100" into the cellphone. 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 and ammunition
Dial "4825550100" into the cellphone. 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" into the cellphone. 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" into the cellphone. 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" into the cellphone. 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" into the cellphone. Note: This phone number translates to "COP-555-0150".

Spawn Annihilator police helicopter
Dial "3595550100" into the cellphone. 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" into the cellphone. Note: This phone number translates to "CAR-555-0142".

Spawn Comet
Dial "2275550175" into the cellphone. Note: This phone number translates to "CAR-555-0175".

Spawn FBI Buffalo
Dial "2275550100" into the cellphone. Note: This phone number translates to "CAR-555-0100".

Spawn Jetmax
Dial "9385550100" into the cellphone. Note: This phone number translates to "WET-555-0100".

Spawn NRG-900
Dial "6255550100" into the cellphone. Note: This phone number translates to "MBK-555-0100".

Spawn Sanchez
Dial "6255550150" into the cellphone. Note: This phone number translates to "MBK-555-0150".

Spawn SuperGT
Dial "2275550168" into the cellphone. Note: This phone number translates to "CAR-555-0168".

Spawn Turismo
Dial "2275550147" into the cellphone. Note: This phone number translates to "CAR-555-0147".

Change weather and brightness
Dial "4685550100" into the cellphone. Note: This phone number translates to "HOT-555-0100".

Map locations
Enter "www.whattheydonotwantyoutoknow.com" into the in-game computers to view maps that reveal all weapon, health, armor, vehicle, pigeon, ramp/stunt, and entertainment locations.

Easy money
Go to an ATM, then cause a traffic jam to the area. Wait for someone to take money from the ATM, then kill him or her. Make sure to block any nearby roads so the ambulance cannot get to the murdered victim. Take the money they dropped on the ground. Then, run a short distance away, and go back. The money should have respawned on the ground. You can repeat this as many times as desired. You can also kill more people taking their money from the ATM to increase the amount of money that respawns. -From: Khairol161

Repairing engine
If the vehicle you are driving breaks down and the engine will not start, call 911, and your engine should start again.

Parking more vehicles
Outside your first hideout is a small parking area to park your vehicles and save them. Instead of parking your vehicles fully within the lines, you can park your vehicles partially within the lines to allow for more vehicles to be parked and saved. -From: Zane

Fast travel
To avoid wasting time driving all the way across the city, call a taxi. They will take you to your destination for your mission, stores, safehouses, or even a waypoint marker. You can skip through the taxi ride, allowing you to travel across the entire city in about ten seconds. This can also be done during missions.

Easy headshots
It is sometimes difficult to get headshots, which do count. With some practice, doing the following is an easy way to get headshots. Press [Auto-Aim], then use the Right Analog-stick to move the auto-aim target around your victim's body. Barely move the Right Analog-stick as you are shooting. This puts bullets in the chest and head, and results in an easy instant kill.

Getting away from police
When running away from the cops, you will have a circular area in which they look for you. However, if you get out and another cop sees you, it changes. To use this to your advantage, barely get out of that circle, which you will see on your radar. Then, just sit there for about five seconds instead of flooring past it.

Regaining health during missions
You can leave the mission area and go to a Cluckin' Bell, hotdog stand, etc. and eat food to replenish your health if you are low and cannot find a health pack. This is especially useful on missions where there are no health packs in sight. Note: You can also take a taxi to those locations during missions.

Avoiding toll booths
Drive through any toll booth with any emergency vehicle with the sirens on. The booth attendant will open the gate, and you will save $5.

$100 for all ringtones and themes
After getting the phone from Playboy X, go to the nearest Internet cafe. Buy all of the ringtones and themes from the ringtones site. Log out of the computer, and you will notice that you only paid $100 for all ringtones and themes.

Easy "One Man Army" achievement
Go to the bridge that takes you to the second island and has a train track under it. Walk along the train track towards the second island before you are allowed to cross the bridge. When you are about half way, you should have a six start wanted level. Then, just stand on the train track for five minutes to get the achievement. You do not have to worry about the police because they will be on the bridge above you so they cannot shoot, and the helicopters are above you so you have cover from them.

Achievements
Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Off the Boat (5 points): Complete the first mission.
One Hundred and Eighty (10 points): In a darts game score 180 with 3 darts.
Pool Shark (10 points): Beat a friend at pool.
King of QUB3D (15 points): Beat the High Score in QUB3D
Finish Him (15 points): Complete 10 melee counters in 4 minutes
Genetically Superior (25 points): Come first in 20 singleplayer street races.
Wheelie Rider (30 points): Do a wheelie lasting at least 500 feet on a motorbike.
Gobble Gobble (10 points): Score 3 strikes in a row, a turkey, in 10-pin bowling.
Driving Mr. Bellic (10 points): Unlock the special ability of taxi.
Rolled Over (30 points): Do 5 car rolls in a row from one crash.
Walk Free (50 points): Lose a 4 star wanted rating by outrunning the cops.
Courier Service (10 points): Complete all 10 package delivery jobs.
Retail Therapy (10 points): Unlock the special ability of buying guns from a friend.
Chain Reaction (20 points): You must blow up 10 vehicles in 10 seconds.
One Man Army (40 points): Survive 5 minutes on 6 star wanted level.
Lowest Point (5 points): Complete mission "Roman's Sorrow".
Over Fulfilled (10 points): Complete all 10 Exotic Export orders.
Manhunt (15 points): Complete the most wanted side missions from the police computer.
Cleaned The Mean Streets (20 points): Capture 20 criminals through the police computer.
Fed The Fish (5 points): Complete the mission "Uncle Vlad".
It'll Cost Ya (5 points): Complete a taxi ride without skipping from one island to another.
Sightseer (5 points): Fly on all helicopter tours of Liberty City.
Warm Coffee (5 points): Successfully date a girl to be invited into her house.
That's How We Roll! (10 points): Unlock the special ability of helicopter.
Half Million (55 points): Reach a balance of $500,000.
Impossible Trinity (10 points): Complete mission "Museum Piece".
Full Exploration (20 points): Unlock all the islands.
You Got The Message (20 points): Deliver all 30 cars ordered through text message.
Dare Devil (30 points): Complete 100% of the unique stunt jumps.
Assassin's Greed (20 points): Complete all 9 assassin missions.
Endangered Species (50 points): Collect every hidden package in the game.
Under the Radar (40 points): Fly underneath the main bridges in the game that cross water with a helicopter.
Dial B For Bomb (10 points): Unlock the special ability of phoning for a bomb to be placed.
Gracefully Taken (10 points): Complete mission "I'll Take Her".
Liberty City (5) (20 points): After meeting all possible friends, the ones left alive all like you above 90%.
No More Strangers (5 points): Meet all random characters.
That Special Someone (10 points): Complete mission "That Special Someone".
You Won! (60 points): Complete the final mission.
Liberty City Minute (30 points): Complete the story missions in less than 30 hours.
Key To The City (100 points): Achieve 100% in "Game progress" statistic.
Teamplayer (10 points): Kill 5 players who are not in your team, in any ranked multiplayer team game.
Cut Your Teeth (5 points): Earn a personal rank promotion in multiplayer
Join The Midnight Club (10 points): Win a ranked multiplayer race without damaging your vehicle too much and with damaged enabled.
Fly The Co-op (15 points): Beat our time in ranked versions of "Deal Breaker", "Hangman's NOOSE" and "Bomb da Base II".
Take It For The Team (10 points): Be on the winning team in all ranked multiplayer team games.
Top Of The Food Chain (10 points): Kill 20 players with a pistol in a ranked multiplayer deathmatch.
Top The Midnight Club (20 points): Come first in 20 different ranked standard multiplayer races.
Wanted (20 points): Achieve the highest personal rank in multiplayer.
Auf Wiedersehen Petrovic (30 points): Win all ranked multiplayer variations, all races and "Cops 'n Crooks", as both sides.
Let Sleeping Rockstars Lie (10 points): Kill a Rockstar developer in a ranked multiplayer match.