When the Internet got relatively mature, sale of any sexual service not involving a minor could be made to anyone not a minor.
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.
Phone sex conversation may take many forms, including: guided fantasy, sexual sounds, narrated and enacted suggestions; sexual anecdotes and confessions; candid expression of sexual fantasies, feelings, or love, and/or discussion of very personal and sensitive sexual topics.
At that time independent phone sex was more dangerous, as Lee's movie portrays.
With the progress of technology it became more practical, convenient, and economical for providers to work out of their homes.
Once means of transmitting payment were developed, phone sex turned into primarily a commercial activity, with customers (overwhelmingly male) and sellers (overwhelmingly female).