Mississippi prison blocked 216,320 illegal calls last month

Phone companies prefer managed-access solutions to technology that jams all cell phone reception in a certain location, which they see as too blunt an instrument.

Steve Largent, president of the wireless association CTIA, said in a blog post on Friday that managed-access technology works more like "a scalpel."

After deploying the technology, a state jail in Parchman, Miss., blocked 216,320 calls last month.

People on jail premises who try to make a call with an unregistered cell phone get a fail message: "The cellular device you are using at the Mississippi State Penitentiary has been identified as contraband and is illegal to possess under the criminal statute, 47-5-193. The device will no longer function."

The technology, approved by the Federal Communications Commission, also makes call information available for analysis so officials can do a deeper dive into who is breaking the rules.

Largent said the technology allows officials "to identify the location of a contraband phone, track its use and provide opportunities to retrieve the device and prosecute those in possession."

President Obama signed a bill into law last month, championed by Sens. Dianne Feinstein (D-Calif.) and Chuck Grassley (R-Iowa), that threatens a year of jail time to people who attempt to sneak phones to inmates.