Phone sex is a conversation between two or more people on the phone where one or more of the individuals is describing the act of sex.
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.
The editor of High Society magazine, Gloria Leonard, is credited with being one of the first people to use "976 numbers", then "900 numbers" for promotional purposes and soon as a revenue stream in the adult industry.
Leonard recorded her own voice informing callers of the contents of the next issue of High Society magazine before its publication.
When the Internet got relatively mature, sale of any sexual service not involving a minor could be made to anyone not a minor.
Software platforms were custom written to handle money collection and transfer, connecting caller and sex worker though neither could see anything but the platform's phone number, and metering the connection.
The telephone companies placed the chat line charges on a customers local phone bill.
If a customer disputed a charge, the telephone company would usually “forgive” the charge but block the caller from calling any other chat lines.
Nevertheless, phone sex should not be confused with prostitution wherein money is exchanged for real life sexual services or physical interactions.