haha sorry. They didn't do any hacking. There are applications out there that you can use and set your phone number as number so caller ID shows up as them.
I'm on Youtube when my buddy pranked me like this. Pretty funny with our conversation. He used a sound board and a bad side of the city party store to prank me and others. My cell was showing the place and a quick map check I had no clue.
Anyhow, they used a software application to pass information through their phone to your caller ID.