Learn to Love Answering Those Voicemails
Your school may have voicemail, a complex answering-machine system that uses a series of recordings to shunt telephone messages to your classroom. You access the system with a numeric or alphanumeric code, given to you by your school (generally changed once yearly).
As with e-mail, answer voicemails the same day they're received. Most voicemails are from parents, concerning grades, homework, discipline, etc. If you ignore these voicemails, parents will tend to get angry. At that point, they may approach the principal, believing that they gave you a chance to discuss their concerns but you never responded. Make certain to respond.
You can also use your school's voicemail system yourself to leave phone messages for other teachers, administrators, and secretaries if these personnel aren't available when you need them; but follow up with a personal visit if you don't get a quick reply. Get up and walk across campus because, even in this age of instant electronic communication, it's always nice to have some face-to-face communication with folks from time to time.
