SpoofCard is the ultimate prank calling tool. It is a phone card that allows you to set the caller ID and phone number you are calling from to be just about anything. You can make a call to RIM and pretend to be calling from Verizon asking when they will be getting the Bold… 
Or you can just use it to scare the hell out of your coworkers by calling from the white house. So far it is completely legal but I would not go around pretending to be law enforcement. It also has a really funny feature that lets you change your voice from a male to female and vice versa. You can even record your exploits!
Check out some of the crazy stories SpoofCard has on their website!!!
Just so you know SpoofCard mentions:
Your financial, personal and call records are all confidential and are untraceable. However, if there is illegal activity and we are served with a subpoena, we will cooperate with the court.
From their FAQ you can use any 10 digit number. Not only will the number show up but also the Name registered for that number would automatically appear.
You can make a free SpoofCard call by using this form on their website to try it out. Let me know how it goes. 
Check it out at: www.spoofcard.com
mo Not Registered
Posted: May 21, 2008 at 7:29 PM EST from my BlackBerry 8310
Will definitely get this on payday….hmm so many ideas for this app(just thinking aloud)
prAnk c@lleR Not Registered
Posted: June 20, 2008 at 2:04 AM EST
man.. SpoofCard rox!
Tiffany Not Registered
Posted: October 2, 2008 at 3:53 PM EST from my BlackBerry 8130
When is Spoofcard going to make ablackberry app? My sis in law has this on her iphone! I hate att I want spoofcar for blackberry!! Please
icantsay Not Registered
Posted: March 4, 2009 at 1:38 AM EST
this app is going to rock the whole bb app world like no other app in history. trust me. sneak preview. http://123spoof.com/bb/download/
N4melessS0ldier Not Registered
Posted: December 22, 2008 at 4:33 AM EST
PhonePhreedom.com is much cheaper than SpoofCard.com
http://phonephreedom.com/