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.
There are still some services that rely upon premium-rate telephone numbers (e.g., 976 and 900 numbers) for billing purposes, although this practice has been largely abandoned due to the high rate of fraud associated with these lines and the inability to dial 900 and 976 lines from cellular phones.
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.
Phone sex takes imagination on both parties' part; virtual sex is difficult if the operator does not put the images in the head of the caller and the caller must be open to the pleasure as well.
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 is the world portrayed in Spike Lee's movie about phone sex, Girl 6.
At that time independent phone sex was more dangerous, as Lee's movie portrays.
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.
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.
The sexually explicit conversation takes place between two or more persons via telephone, especially when at least one of the participants masturbates or engages in sexual fantasy.