Complex sentence: During the first half of the 20th century it was widely used for transoceanic telephone and telegraph service and business and diplomatic communication, but due to its unreliability shortwave skip communication has been mostly abandoned by the telecommunications industry.
Split into simpler sentences: During the first half of the 20th century it was widely used for transoceanic telephone and telegraph service, and business and diplomatic communication. Due to its unreliability, shortwave skip communication has been mostly abandoned by the telecommunications industry.