In its request, the EFF cited a patent application by Bharat Doshi and other researchers from Lucent Technologies, "ATM network architecture employing an out-of-band signaling network," which was filed in 1994. They were granted Patent No. in 1996. That application covers many of the same developments in the C2 patent but was never cited by the applicant or the patent office examiner when C2's application was being reviewed, EFF said.

EFF believes part of the problem is that the U.S. Patent and Trademark Office is overburdened by applications covering increasingly complex inventions.

"I don't think that they have the time or the resources that they need to be able to give ... the right kind of thorough evaluation to every patent request," Cohn said. "We're just not living in Benjamin Franklin's time any more."

Lawsuits over this patent couldn't sink the VoIP industry, because it's so well-established, IDC analyst Will Stofega said. But that kind of litigation can slow down advancements while companies fight in court rather than the marketplace, he said. Stofega cited the long battle between Research In Motion and NTP, a case that threatened a shutdown of BlackBerry service several times before it was settled out of court in 2006.

C2's Weintraub downplayed the EFF's effort to have its patent invalidated.