Instructions
Load any "Grand Theft Auto IV" game save file. Press "Up" when the game loads to take out your cell phone.
Scroll down and select "Multiplayer" and then "Player Match" or "Party Mode." Player Matches are open to anyone, although you can reserve a team spot for your friends. Party Mode is only accessible to those you choose to invite.
Press the "PlayStation" button on the controller to invite friends while waiting in the game lobby. Scroll to your friends list and select the friend you wish to invite.
Press "Up" to access the cell phone if you want to invite a friend during a match. A list of your friends is displayed on the phone. Select a friend to send an invitation to them.