We have all played the game 20 questions. I think it would be a great learning experience for kids in elementary students to connect on Skype in a game of 20 questions.
Using the game 20 questions, and not knowing the other classes location, each class will will ask a geography question that will be replied with a Yes or No. An example question might be: "is your city located in the United States." Then the opposing class will repeat. A back and forth will continue until one class guess correctly.