Phone sex
Phone sex is when two or more people talk about sex over the telephone. The idea of the call is to sexually stimulate the caller by being explicit. All of the people taking part do this voluntarily. Typically, phone sex is used for masturbation. Phone sex  between two people is as old as there are telephone lines, which did not require an operator. It started in the 1930s. Starting with the later 20th century, there are also commercial phone sex lnes, where a sex worker is on one end of the line.