Vistors smuggle them in. Guards sell them. Family or friends toss them over fences. 
No, not drugs, but something authorities are saying are much more dangerous: Smart Phones.
Check out today's New York Time's fascinating article, "Outlawed, Cell Phones Are Thriving in Prisons" here.
Offered in the article is also a brief commentary on why limited use of cell phones might be helpful in assisting prisoners' reentry.
