The provider provided (say) 10 minutes of service, but got to keep all of the money (say 20 minutes).When the Internet got relatively mature, sale of any sexual service not involving a minor could be made to anyone not a minor.Originally phone sex services consisted of a managed network of dispatchers (live or automated) and erotic performers.Performers would come to a studio where they received a cubicle, coaching, and cash incentives to keep callers on the line longer.
(This attitude still survives among some providers.) When public (mostly female) pressure forced the phone companies to stop providing this service to sex workers, a transition was made to a manual method: pre-paid blocks of time, 10, 30, 60 minutes, whatever the customer would pay for.
He removes his clothes and lies on the floor and takes her on him.
She guides his penis into her hairy pussy and begins to ride him. Finally, she takes his whole dick into her mouth and begins to suck it nicely.
With the progress of technology it became more practical, convenient, and economical for providers to work out of their homes.
Human dispatchers — female, except for gay male phone sex — answered the advertised phone numbers, processed payment via credit card, chose who of the available performers in the dispatcher's judgment best matched the clients' fantasy (grandma, black girl, college girl, etc.), and connected the client with the provider. Either could hang up, though some services put economic pressure on providers not to do so.