This demo application is written in Ruby, using Tropo’s Scripting API. The outbound phone call is placed when your application invokes Tropo's API URL with your token. It’s using $numberToDial as the variable to pass the destination phone number parameter in, which is sent along with the token string in the REST request. You can find more information on passing in custom parameters to a Tropo application here: https://www.tropo.com/docs/scripting/quickstarts/sending-text-messages/passing-parameters