Cellphones in prisons

I found the following article very interesting.
“Technology is changing life inside prisons across the country at the same rapid-fire pace it is changing life outside. A smartphone hidden under a mattress is the modern-day file inside a cake.” Outlawed, Cellphones Are Thriving in Prisons. The New York Times Cellphones, Though Banned, Thrive in U.S. Prisons - The New York Times