...from the website...
SPOOFEM.COM offers you the ability to change what someone sees on their call display when they receive a phone call. This is typically referred to as "Caller ID Spoofing" or "Call Display Spoofing".
You can show any phone number you wish on their call display. You can change your voice to male / female, record the conversation, SMS text message and be able to protect your privacy by not showing your number on their caller ID. (more)
There are other spoof options, too.
• Prepaid virtual calling card (free test call)
• SpoofCard Widget (free test call download for Mac OS X)
• Telespoof (free test call)
• Spooftel
While spoofing is currently legal, it may not be in the near future. Laws against it are in the works.
• H.R. 5304 [109th]: Preventing Harassment through Outbound Number Enforcement Act
• H.R. 251: Truth in Caller ID Act of 2007
If spoofing becomes illegal should you believe your Caller ID again?
No.