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).
The incentives for providers were then reversed; rather than earning money from keeping the customer on the line (orgasm delayed), they earned more from bringing the caller to orgasm quickly, so as to move on rapidly to another call.
Unused minutes were rarely usable on a second call.
Verizon provided billing services to calls made in Massachusetts, Rhode Island and Maine.