International telephone calls are those made between different countries. These telephone calls are processed by international gateway exchanges (switches). Charges for these calls were high initially but declined greatly during the 20th century due to advances in technology and liberalization. Originally they were placed via long-distance operators. The calls were transmitted by cable, communications satellite, radio, and more recently, fiber optics and Voice over Internet Protocol (VoIP). International Direct Dialling was introduced in the 1970s, so calls can be dialed by country code without an operator.