Back in 1989 during my computer courses at Seneca College in Toronto, a fellow student (
who worked for Bell Canada) brought a few hundred yards of phone cable in to the computer lab after hours one night. No instructors or faculty were around.
We were running new 386sx PC's at the time. We opened a ceiling panel in the lab and had another student climb through the ceiling joists...make his way about 50-60 yards to the Dean's office with the phone cable...and wired it in to her phone jack. He somehow hid the cable so it went undetected.
Back in the lab, we hooked the cable to a 2400baud Zoltrix modem and started dialing adult BBSes throughout the U.S. - one in particular I recall in Simi Valley, CA. The guys amused themselves downloading a ton of adult GIF files at 2400baud for a month or two, before we decided to pull the plug.
We found out much later the Dean's phone bill was over $2,600.
And they never found out why.