VM Inline Voice Magnifier
Used with a telephone, the VM Inline Voice Magnifier can add up to 25dB of gain to the user's voice. It works well for those who can only whisper or have a very soft voice. Simply connect it between the receiver and base of a corded telephone. Includes a telephone receiver cord and 9V battery.
More information: http://www.harriscomm.com/index.php/vm-inline-voice-magnifier.html