Why are the inmate calls not free?

I want to know why an inmate in the county jail or correction facility would have to pay for a phone call if they have had no way of getting any funds to pay for a phone call it's not fair. From a personal experience my mother was just placed in the correctional facility in our county today and she was trying to make a call but it was tell me and my step dad that we would have to make payments but my mother was just booked today how are we suppose toting her and my 4 siblings if she is only in for 2 days we wanted to receive the calls but we couldn't. It's very frustrating for me and my family especially if we are already slightly struggling financially I would just like somebody to listen and understand our frustation. If anyone can give me onsite on the easiest way to get calls that won't charge please let me know thanx for your time