That means that law enforcement could lose records of who was called and when, and possibly miss entire call recordings as well, Sherr said.

Back in 2005, the FBI downplayed the Penn team's loop extender research, saying that it applied to only about 10 percent of wire taps. The J- standard studied in this paper is much more widely used, however, Sherr said. An FBI representative did not return messages seeking comment for this story.

The researchers wrote a program that connected to a server over Sprint's 3G wireless network 40 times per second, enough to flood the Call Data Channel. They say that they could get the same results by programming a computer to make seven VoIP calls per second or to fire off 42 SMS messages per second.

These techniques would work on mobile phones or VoIP systems, but not on analog devices, Sherr said.

Because the researchers weren't able to test their techniques on real-world systems they don't know for certain that they could thwart a wiretap. But Sherr believes that "there are definitely dangers" in the way the standard is written. "Because it's a black-box system, we don't know for sure."