Spoofing

Caller ID is a simple string of data that can be read and generated very simply by small computer programs and even some inexpensive devices. Although the caller ID information is transmitted in between the first and second rings, before the phone call is connected, it is possible to mislead the phone company as to the origin of the call, thus defeating caller ID. Although misleading the phone company by generating ANI code or by other electronic means is very complex, simpler means do exist. Using services like Vonage or Skype, calling from a payphone, or using a calling card are easy means to fool caller ID.