This is pretty rudimentary, but a classic. Call someone up once or twice a day as different people, each person asking for the same person. Example: Person 1: Is Tim there? The Mark: No... There is no tom here. Person 1: Can You just tell him, Rob called? *Click* Person 2: (With an accent) Is Timothy there? The Mark: No, No tim here. Person 2: Well, if he is, just let him know I'm looking for him. After about a week of this, call up as Tim, and let the fun begin.