"You could use this in a concert hall, allowing cell phones to work before the concert and during breaks, but shutting them down during the performance," said Michael Riedlinger, president of NaturalNano.

Using nanotechnology, particles of copper are inserted into nanotubes, which are ultra-tiny tubes that occur naturally in halloysite clay mined in Utah. Combined with a radio-filtering device that collects phone signals from outside a shielded space, certain transmissions can proceed while others are blocked, the Chicago Tribune reported.

However, the wireless phone industry is up in arms over the development.

"We oppose any kind of blocking technology," said Joe Farren, spokesman for The Wireless Association, the leading cell phone trade group. "What about the young parents whose baby-sitter is trying to call them, or the brain surgeon who needs notification of emergency surgery? These calls need to get through."