Quite a while back, there was a very popular AMP girl, Ting Ting, who managed (she claimed some guy owned it, but I always had my doubts) a parlor in Hicksville. She was a doll and very well reviewed. The place was always busy. When she felt comfortable with a client, she gave him her cell number that made access easier. Now, I don't know if it was really her private cell number or just another number that the business used for pre-screened customers, but she made it seem like only special people got it, an interesting marketing ploy. I never got take-out with Ting Ting.
On the other hand, I've been given private numbers from girls who clearly did it on the sly to pull business away from the house on the side. It can be used both ways.