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).
Verizon provided billing services to calls made in Massachusetts, Rhode Island and Maine.
AT&T and MCI offered nationwide collection services, with a cap of $50 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.