Ok, first off let me say that caller ID spoofing can be done with the use of this service --->
http://www.moofind.com (referral link). It's 0.05 per minute, and lets you record calls (downloadable in WAV format), dial long distance for free, etc. It completely masks your phone number, and displays it as whatever you want. It is also completely untraceable.
Here's a sample prank call that was done with it... calling Domino's Pizza using Pizza Hut's phone number:
http://www.tindeck.com/audio/my?loc=...20Shitting.mp3
Now that that's out of the way, here's ways to have fun with it:
1. If you call someone's cell phone using their own phone number, and they don't have it set to require a password from their own # (80% of people are vulnerable), you can get into their voicemail control menu! This means you can listen to their messages, change their greeting, change password, etc. Very awesome.
2. If you call many Pizza places or fast food restaurants from a corporate office, you can social engineer them into giving ____ for free to ____ person. This also works with movie rental places and more! Just experiment.
3. If you call someone from a phone number that is registered with a phone company, it displays the person's name who it is registered to on their caller-ID! Check
http://people.yahoo.com to find cool names/numbers to use, also... here are a few that you can use:
Gaylord Focker
3017020226
Britney & Whitney Spears
2566379093
Devil, A
7074510855
Church O God
5089990483
Hulk Hogan
9313624147
Jesus
2127950662
Freddy Krueger
6084625459
A Dick
2033301920
Chong Bum
9252563696
Kakin But
7187483923
Man I Ho
6262896233
I Gay
5854530469
Crazy
6612851699
Bill Gates
5183929384
Pearly Gates
8043789099
Hugh Jass
2126771573
Bill Clinton
9167264257
Luke Skywalker
9043967991
Darth Vader
7739295770
Annikan Skywalker
3306285301
Micheal Moore
7344804159
Bart Simpson
3176878655
John Kerry
9786887186
John Ashcroft
3154934241
Yao Y Ming
7188881156
Don King
8143953859
Micheal Tyson
6267977287
Derek Jeter
6125885880
Laura Lesbo
6018991464
Laura Bush
8149408339
M Lewinsky
2163211828
Fred Flintstone
7707207760
W Flintstone
3052552568
I would post more, but that was too long as is lol...
4. Prank calls - this is obvious, if you call someone from 'Jesus' or 'The White House' or '911', it increases the hilarity factor.
If anyone does this, share the recordings! I'll try to upload some more of my own.