47 CFR §68.6

As of January 1, 2000, all telephones, including cordless telephones, as defined in § 15.3(j) of this chapter, manufactured in the United States (other than for export) or imported for use in the United States, must have volume control in accordance with § 68.317. Secure telephones, as defined by § 68.3 are exempt from this section, as are telephones used with public mobile services or private radio services.