Don't go making phony-calls! Please, stick to the seven digit numbers you are used to. Yes that was a quote from a Weird Al song, and yes it is topical. The U.S. Congress has just passed a most unfortunate law that bans caller ID spoofing nationwide. A thousand little would-be Bart Simpsons are crying for the world they've lost right now.
Ars Technica reports that the Truth in Caller Act of 2010 makes it illegal to “cause any caller ID service to transmit misleading or inaccurate caller ID information, with the intent to defraud or deceive”. Blocking your own outgoing info is still fine, and law enforcement can still spoof numbers, The police can (apparently) defraud and deceive all they want.