Steins;Gate: Linear Bounded Phenogram

Linear Bounded Phenogram is a visual novel in which the player advances through text and dialogue to read through several short stories; by using the player characters' cell phones to make different choices and responses in the "phone trigger" system, the player can affect the direction of the game's plot. In the iPhone version of the game, the player picks up and puts down the in-game phone by holding the phone they are playing on vertically or horizontally, respectively.

Source: Wikipedia, "Steins;Gate: Linear Bounded Phenogram", available under the CC-BY-SA License.