Friendships in GTA IV
After you do so many missions for someone, eventually they will call you and ask to hang out. From that point onward, you can call them to set up times to hang out. Hanging out with your friends is a fun way to work on your relationships with them so that eventually you can get their "friend benefit".
Bowling Pool Strip Club Cabaret Club Darts Drinking
note: sometimes your friend will NOT be able to perform their service for you.
Little Jacob - drives to your location with a trunk full of guns for you to purchase. Roman - sends a cab to pick you up and take you anywhere for free.