The contract, worth $2.8 million, is for General Dynamics to integrate a new public switched telephone network technology to the NSA Sectera vIPer secured phone. Officials say the new network technology is an effort to securely connect vIPer phones with unsecured telephone lines.

The secure vIPer Phone is the NSA's voice-over Internet protocol phone certified to send top secret classified information over the network. With the PSTN added to the vIPer phones, officials will be able to use either VoIP networks or the PSTN.

"The idea behind PSTN Connect is to provide users with a flexibility they don't have today," John Cole, General Dynamics C4 Systems vice president of information assurance, said in a statement.

"It's about protecting our customers' investments by providing a product that will accommodate evolving communications technologies."