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Once means of transmitting payment were developed, phone sex turned into primarily a commercial activity, with customers (overwhelmingly male) and sellers (overwhelmingly female).
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.
Originally phone sex services consisted of a managed network of dispatchers (live or automated) and erotic performers.
AT&T and MCI offered nationwide collection services, with a cap of per call.
The vast majority of modern services in the United States use toll-free numbers whereby clients can dial up to request a call with a particular performer using credit cards, Automated Clearing House systems, and a variety of other billing methods.
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.