My dad and his buddy devised a plan to get unlimited calls from phone booths to abroad. They drilled a 2 Deutschmark coin and put a fishing line through it. They figured out that the coin only drops after the allotted time is up, allowing the machine for there to be credit registered. But there was nothing preventing the coin from going upwards again. So they just kept pulling it out and then inserting the coin again. And re-dialing the international number. Like some petty comic book villains.