Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Voice modem is a term commonly used to describe an analog telephone data modem with a built-in capability of transmitting and receiving voice recordings over the phone line. Voice modems are used for telephony and answering machine applications. Similar to the Hayes command set used for data modems, in which the host PC commands the modem via a series of commands known as AT commands, there exists a well-defined set of common voice AT commands that are somewhat consistent throughout the industry. Because voice mode is not the prototypical use for a modem, many modems on the market have poor or buggy support for their voice modes. Characteristics of a good voice modem depend greatly upon the intended application, and include: