Back in the day when every phone had its own wire pair and caller ID wasn't around to spoil things, I was living in the dorm, and had the means to tap into a second circuit. I patched the two lines together through some switches and a matching transformer that I had rigged up. I had fun connecting two unsuspecting outside people to each other, each blaming the other for calling. The best was when I simultaneously dialed the operator on both lines.
Operator 1: "Operator, may I help you?"
Operator 2, picking up the line: "This is the operator."
Operator 1: "Yes it is."
Operator 2: "May I help you?"
Operator 1: "Are you having some difficulty?"
Operator 2: "No ma'am, who are you trying to reach?"
Operator 1: How may I complete your call?"
Operator 2 (realizing she's talking to another operator, and taking an air of superior knowledge): You need to disconnect your call before looping into another exchange."
[click]
I'm rolling on the floor.