Phone Sex

I had someone call the other day and requesting to pre pay some way to have phone sex.
Got me wondering what the legal side of that would be.
I have done that for different companies in the past and they paid you for your services, so was wondering is that against the law for someone paying for those kind of services if someone set up a way for a person to prepay with a prepaid card?
Just curious if anyone had any dealing with this on their own and not working for a company?
thanks
Perfectly legal. Use to do it though, because Paypal will shut you down for it.