It was a very common hack when I was in school that, to call home, you'd make a person to person call and your parents would decline--saying the person you were calling for wasn't there--and then direct-dial you back.
[ADDED: And I'm sure there are people reading that comment with puzzled expressions who have no idea what I'm talking about. :-) ]
If I remember correctly, making a collect call through your telephone company required talking to an actual operator who would set up the call and inform the receiving party of who was calling. The 800 number collect call services that eventually sprung up all used automated systems and they were perfect for this kind of abuse. You had about ten seconds to blurt out your message before the recording would stop.
I used to ride the Greyhound to visit my dad on weekends, and it would stop at a truckstop about ninety minutes away from my destination. At first I had to carry a pile of quarters to make the long distance payphone call to let him know I was on my way, until we finally figured out I could just blurt "Dad I'm in town xyz, be there in 90" instead of my name. Saved me a buck fifty or so every trip.
If you called 1-800-COLLECT, you would deal with an automated system, not an operator. I would use this as a free signal for when my dad should pick me up from after-school activities, but in my case it didn't require putting in a message, he just knew if he was getting a collect call from me to head out soon, and in any kind of emergency I would just use the change in my pocket.
There was a time in the early 90's when you could make a long distance call from a residential number and get AT&T to bill it to a third number without their consent. I guess the idea was that if there was a dispute they would go after whoever originated the call. What they didn't account for was the rise of COCOTS or Customer Owned Coin Operated Telephones, which were payphones connected to normal lines where all of the security was local instead of at the telephone company office. Long story short you could make long distance calls from a lot of payphones and bill them to random strangers.
I'm in my late 30s and I remember one other reference to a "person to person call" - I think it was a Simpsons episode from when I were the one making calls from school!
FYI for others, in the US at least a "person to person" call was an operator-assisted call in which you didn't need to pay if the person you were supposedly trying to reach wasn't available.
And a collect call meant that the party receiving the call was the one who paid. Collect calls at least still exist. I've used them when calling a credit card company from overseas.
("Don't cheat the phone company, save money the legal way.")
I think the GEICO one is the most posted on the Internet because I also remember the same conceit for one of the "direct access long distance" numbers (Sprint's 10-220) and for, I think, 1-800-COLLECT.
[ADDED: And I'm sure there are people reading that comment with puzzled expressions who have no idea what I'm talking about. :-) ]