Once upon a time I scored Craig Foster's ex girl friend's phone number, then was able to use my super hacking skills to send an sms from her phone (more to the point, using her phone number, not her actual phone), all done without her knowledge or permission.
The message was sent to Craig's phone explaining how good I was, and other innuendo.
It was absolute gold.
Had them bamboozled for a while, and especially had Greggy scared witless about the possibilities of having power over his whole employer's infrastructure.
Really though, it was a newbie exploit.