The Hammacher Schlemmer Institute rated this The Best corded clarity-enhancing telephone available for its sound quality. Its patented digital technology uses two volume control buttons to increase the volume of an incoming caller's voice up to 55 dB by amplifying high-frequency sounds and reducing low-frequency noise that causes interference and distortion such as air conditioning or static, creating a clear sound more conducive to conversations. Unlike lesser models that only adjust for volume or completely eliminate low-frequency sounds, it provides a full range of frequency adjustment for richness of sound. Its speakerphone provides unambiguous sound, so messages from the built-in answering machine are heard easily. It has a 2.5mm jack for hands-free operation using a headset (not included). It has large, easy-to-read numbers and eight one-touch dialing buttons (including an emergency button) that accommodate cut-out photographs. It also has a flashing ring signal, and an adjustable ring tone/volume control. Built-in caller ID records up to 30 calls. 2 1/4" H x 8" W x 8 1/2" D. (4 lbs.)