If you wanna get away with calling in a bomb threat, just call up a bank or something from a public phone and tell them there is a bomb in your school. They will have to call up the school and tell them theirselves. Ingenious I know!

Just make sure you don't use a rarely used public phone, and if you do, don't leave any prints and make sure your car is parked far away and that you have to go into woods to get to and from the phone being used (to avoid someone picking you out). Also wear clothes that you can throw out/burn and covers your face.

Make sure there are no cameras by the phone either. Its pretty damn easy to call in bomb threats, but you can get in deep shit for it...