Players must pay for their services. The sound produced when a car shakes with the player and a hooker inside in Vice City. Honking isn't necessary in order to get a prostitute in the car. Players can only have "sex" with them on any ground that can kick up dirt or sand, and even surfaces like the tiles of swimming pools, as the game doesn't consider seclusion as a factor. Having "sex" with a hooker is just an effect of the car bouncing up and down on an accelerating speed specifically, the car lowers down on where the hooker is sitting.