Quote from  Blog January 13th 2008 @10:17am from sbw07:
“I tried using it ( spoofing) to confuse a friend by having his own cell # show up on the call instead i confused the cell phone /upon seeing his own caller id the system ( sprint) assumed that the owner was trying to check his voice mail.  so i was let into his message box without a password- i was able to listen to all  his messages!”

In 2007 there was legislation passed in the US that makes Caller id spoofing illegal