Wikipedia:
International call
International Calls are made between different countries. The calls are processed by gateway exchanges (switches). The rates for
these calls were expensive but are now cheaper due to advances in technology. Originally they were placed via operator. The calls
were transmitted by cable, satellite, radio, and more recently, fiber optics and VOIP. IDD or ISD (International Direct Dialing)
was introduced in the 1970s, so calls can be dialed without an operator.
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