A friend of mine 2 years ago connected his paypal account on skype and got 1 month free of credit and could call any phone number in many countries worldwide for free. In skype you can have many calls at the same time so most of the times we rang 2 random numbers and the strangers started arguing about who called in the first place lmao. But the best prank we did was to call a pizza place, make a big order, ask them to repeat the order "to make sure it was correct" and when they started saying the order we called another pizza place so when the guy from the 1st call was done the other pizza guy, who wrote down the "order" the 1st guy was repeating, was asking for the address and then just confusion lmao