This article explains how managed access systems (MAS) can prevent inmates from using cellphones smuggled into correctional facilities as contraband. Rather than relying on keeping contraband phones out of a facility, MAS can keep inmates from making phone calls to phones outside the facility. Cellphone calls from inside the facility are allowed for only permitted users. Phone numbers not on the permitted-user list are denied access to cellphone services by MAS; however, MAS technology is unable to stop the use of Wi-Fi to access the internet. Still, loss of the ability to make calls or send text messages has the potential to make contraband cellphones less valuable and reduce demand. The installation of a MAS requires approval from the FCC and carrier consent for deployment. Also, they have the potential to cause interference outside of the prison or to adjacent bands unless properly designed. The two reports on which this article is based present case studies of MAS used in the Mississippi State Penitentiary and two jails in Baltimore (Maryland). This article provides online access to the full reports on these case studies.