With the progress of technology it became more practical, convenient, and economical for providers to work out of their homes.
Software platforms were custom written to handle money collection and transfer, connecting caller and sex worker though neither could see anything but the platform's phone number, and metering the connection.
Details vary significantly from one platform to another, but the provider may be given a personal page on the platform to use however she (sometimes he) wishes.
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.
She is so wet by now, she won’t have any problems masturbating and cumming several times in front of the camera.