Although prison officials have long battled illegal cellphones, smartphones have changed the game. With Internet access, a prisoner can call up phone directories, maps and photographs for criminal purposes, corrections officials and prison security experts say. Gang violence and drug trafficking, they say, are increasingly being orchestrated online, allowing inmates to keep up criminal behavior even as they serve time.

“The smartphone is the most lethal weapon you can get inside a prison,” said Terry L. Bittner, director of security products with the ITT Corporation, one of a handful of companies that create cellphone-detection systems for prisons. “The smartphone is the equivalent of the old Swiss Army knife. You can do a lot of other things with it.”…

In Oklahoma, a convicted killer was caught in November posting photographs on his Facebook page of drugs, knives and alcohol that had been smuggled into his cell. In 2009, gang members in a Maryland prison were caught using their smartphones to approve targets for robberies and even to order seafood and cigars.