Season 3 episode 2: Breaking Up Is Hard to Undo; Kelly leaves an angry answering machine message directed toward Zack which he plays for Slater in the boys locker room.
Season 2 episode 8: Rent - A - Pop; Zack comes to the realization that there is only one way to reach out to his father Derek: mobile to mobile.
Season 2 episode 8: Rent - A - Pop; Zack tries to have a serious confrontation with his father but Derek keeps getting distracted by phone calls.
Season 2 episode 4: Driver’s Education; Zack tricks Screech into doing his Mr. Tuttle impersonation over the phone to stall Mr. Belding.
Season 1 episode 20: Screech’s Birthday; The girls call Mr. Belding pretending to be a student who has multiple personality disorder and is lost in the mall.