Due to the potential for emotional intimacy between those who have engaged in phone sex, it is a matter of some debate whether phone sex is to be considered infidelity when involving a person outside of a committed personal relationship.
In concept they have a lot in common with platforms such as Ebay: the seller provides the picture(s), description, and sets the price, a percentage of which is kept by the platform.
In the sex industry, similar platforms emerged facilitating the selling of used panties and other odoriferous garments, and for "cam" video sessions, in which the customer, for a fee, can direct the woman on the video screen, and for a higher fee, have a private connection (no one can see caller or provider except each other).
By the end of the 1980s, nearly all of the major local phone companies in the United States, plus the major long distance carriers, were actively involved in the adult chat line business.
Performers would come to a studio where they received a cubicle, coaching, and cash incentives to keep callers on the line longer.
This is the world portrayed in Spike Lee's movie about phone sex, Girl 6.