In the mission when you have to rescue Truth's friends, one of them is Kent Paul from Grand Theft Auto: Vice City. The old man who runs the casino that you later meet in the mission is Ken Rosenberg, Tommy Vercetti's lawyer in Grand Theft Auto: Vice City, and mentions Tommy and the "good old days" in an intermission sequence.

Walk into an Ammu-Nation and listen carefully. You can hear a commercial that was featured in Grand Theft Auto: Vice City. It says "The store leading the fight against communism is having a blowout sale! Ammunation has a wide selection of Peace Makers! Come by Ammunation on Militia Mondays... "