The phrase "a secure telephone" is correct and usable in written English.
It can be used when referring to a telephone that has features or technology designed to protect the privacy and security of communications.
Example: "For sensitive discussions, we should use a secure telephone to ensure our conversation remains confidential."
Alternatives: "a protected phone" or "a safe communication device".
Much of the information was sent directly to top officials from John McLaughlin, the acting C.I.A. director, who spoke with Frances Fragos Townsend, President Bush's domestic security adviser; via a secure telephone line, he could instantly reach her with the press of a single button.
For example, the KGB set up secret acoustic laboratories dedicated to creating a secure telephone system.
Then, using a secure telephone line, he called Mr. Moon early in the morning in Seoul to get his approval.
Mr. Obama excused himself to get on a secure telephone line installed just for his visit in case of emergencies like this.
A senior terrorism official at F.B.I. headquarters telephoned Pasquale J. D'Amuro, the head of the F.B.I. office in New York, on a secure telephone line.
Three communication networks relay information between the RAF ground station in the UK and the UAV: "a secure internet-based chat function, a secure radio routed via satellite and a secure telephone system".
Some Qaeda lieutenants used cellphones only to arrange a conversation on a more secure telephone.
The episode again threw the spotlight on Mr. Pruitt, who is facing multiple allegations of unethical behavior, including the purchase of a $43,000 secure telephone booth for his office, the rental of a condominium from the wife of an energy lobbyist with business before the agency and his habit of flying first-class to places including Morocco, where the E.P.A. has no official business.
Until further notice, Apple users will only be able to reset their passwords online and not over the telephone with an AppleCare specialist; the company is apparently working on a more secure telephone password reset method, and until that method is complete, password resets will be online-only, through the company's iForgot service.
The calls to foreign leaders, which are primarily made from a highly secure telephone at his desk in the Oval Office, are standard fare for all presidents.
Mr. Pruitt is the subject of at least 13 federal investigations, and a government watchdog agency concluded that he had broken the law with his purchase of a $43,000 secure telephone booth.
