Caller ID Spoofing
Prank calls and staying anonymous are some of the most used reasons for caller ID spoofing but there are far better ones which give legitimacy to the whole caller ID spoofing practice.
Professionals can use these services to make their office number appear when calling clients or potential clients from their personal cellphone's or home numbers. While *67 is a free service to prevent your caller ID from beening seen this is easily defeated by simply routing the number to a toll free line which reads past the simple block for billing purposes. In addition, several companies have "Anonymous Call Rejection" features which prevent "Private" numbers from ringing the intended recipient. By simply entering in 555-111-2222 using a service like SpoofTel would allow the call to continue as it is not "Private" or "Blocked".