In AiD3, there is an Easter egg referencing the bell that is never used. If the player were to call a number on a bathroom stall, they would get the answering machine for a bell cleaning company. The person talking would say that there is nothing that he hates more than someone carrying a bell around with no purpose, which is exactly what the player does every game.
In AiD3, one of the numbers on the bathroom walls is for someone named Boris. If the number is called, it plays the song from the first Alice is Dead. If the player enters the middle stall after calling that number, the Rabbit will receive a text message saying "Alive Slice". Mix the letters around and it becomes "Alice lives".
At the very end of the game, look as closely and carefully as possible at the letter "The end". You will see a question mark appearing after it (though you will be led to the main menu screen no more than 0.5 second soon after that). Some people speculate that the game developers seem to announce about the releasing of another game of this series by that.