Call spoofing is similar to ip spoofing or mac spoofing where u can display any number of ur choice instead of displaying ur number .You can call your college prinicpal threatening him saying that there is a b0mbin da college .You can use this technique as long as u use it for fun but it is not acceptable for anti social activities and finally u will b ending up in prison.
If u want to know more about this goto this link
http://en.wikipedia.org/wiki/Caller_ID_spoofing
there are some sites that give you a initially free call spoofing service to test, here are some call spoofing sites:
